I believe Jack the Giant Killer may have again provided further inspiration for the giant chief, to either Gygax or Fletcher and Pratt. Consider the following:
“He beheld a giant sitting upon a block of timber, with a knotted iron club by his side. His goggle eyes were like flames of fire, his countenance grim and ugly, and his cheeks like a couple of large flitches of bacon, while the bristles of his beard resembled rods of iron wire.” 
And too, an illustration by Arthur Rackham portraying the giant Galligantua seems to be a perfect source for Gygax’s completed conception of chief Nosnra. 
The fortress-dwelling — the “Steading” itself — is also nicely depicted in pictures, and in the module’s maps as well. This settlement which Nosnra and his tribe reside in is similarly inspired in part by The Roaring Trumpet. A steading, at its simplest, is defined collectively as a farmhouse with its outlying buildings. Nosnra’s more substantial domain however is a “great timber fortress,”  built at the northern end of a dirt road. Beyond, the higher peaks of the Jotens channel waters toward a pond, which is situated down in a hidden valley a mile to the north. 
Trumpet and a nod to Bulfinch provide the formative inspirations for this fortress, where Utgardaloki’s Utgard Castle is described as being “cruder [than a previously seen log house], made of logs with the bark on, and vastly bigger — as big as a metropolitan railroad terminal.” 
Gary’s background information in G1 informs us that any adventurers who assault this Steading shall be rewarded by being allowed to keep whatever they may find, even though the giants have pillaged all of their ill-won riches from innocent folk throughout the countryside. This straightforward missive, too, may have been lifted by Gary from Jack the Giant Killer, as retold in English Fairy Tales (1918) by Flora Annie Steel, where we read:
“It so happened that one market day Jack, then quite a young lad, found the town upside down over some new exploit of the giant’s. Women were weeping, men were cursing, and the magistrates were sitting in Council over what was to be done. But none could suggest a plan. Then Jack, blithe and gay, went up to the magistrates, and with a fine courtesy — for he was ever polite — asked them what reward would be given to him who killed the giant Cormoran.
‘The treasures of the Giant’s Cave,’ quoth they.
‘Every whit of it?’ quoth Jack, who was never to be done.
‘To the last farthing,’ quoth they.
‘Then will I undertake the task,’ said Jack, and forthwith set about the business.” 
The D&D characters who play in the G1 module, of course, are tasked with precisely this mission.
On the evening of the adventurers’ first raid, there are only a few guards posted at the gate because chief Nosnra is hosting a huge celebratory feast in honor of his powerful guests. The unsupervised guards have gotten drunk and passed out at the front door. The sentry in the watch tower is asleep as well, which explains how the adventurers can simply come right up to the front door if they’re foolish enough to choose that open path.
A little deeper inside the fortress we glean a further idea of the hill giants’ crude, callous nature inside their dormitory, where the children are sequestered during the evening revelry: these big (human-sized!) urchins “are rollicking, and beefy smacks, laughter, etc. are easily heard.”  Gary quite enjoyed the possibilities implied by this inclusion of giant children. He even set up a possible scenario where clever players might choose to impersonate the young hill giants, but no one ever seems to have done this.  In setting up this prospect, Gary may have been inspired by a specific incident in The Roaring Trumpet, where Heimdall stuffs his furs with straw in an attempt to look bulky and giant-like so that he can escape capture outside the fortress (it doesn’t work). 
Following from the dormitory, the major set piece in Nosnra’s Steading is the great hall, which was similarly inspired by its portrayal in Trumpet. There, we read that the chief’s hall is “filled with giants, [who are] drinking, eating, shouting at the tops of their voices.”  A whole ox is roasting in the fire pit, with room for other tasty livestock too (burgers, chops, and bacon!). In describing this colorful scene, Gary may have also borrowed a bit more from Jack the Giant Killer and altered the details. There, we read:
“ … [Jack] came to a huge hall paved and roofed with freestone. At the upper end of this was an immense fireplace where hung an iron cauldron, the like of which, for size, Jack had never seen before. … Here it was that the giants used to dine.”
In the midst of the great hall, the feasting chief Nosnra is entertaining an evil cloud giant (the likely guest of honor) and also three stone giants, who might be emissaries from a nearby clan. Nosnra is probably trying to win over the stone giants from their austere and unyielding True Neutral philosophy, perhaps by posing the raids as being part of a larger ongoing conflict between the irksome feudal mortals and giantkind. (A little ale and mead help matters along.) The stone giants might be a nod to a scene in The Hobbit, but knowing Gary’s preference for non-Tolkien sources, he might also be referencing Norse mythology once again. It seems probable that these stone giants are also a nod to the leir-jotnar, or clay giants; and the villainous Thor-foe Hrungnir who had a head, heart, and shield all made of stone. 
Beyond these interesting guests, there are many other evocative monsters who serve the giants within the Steading. Nosnra and his tribe-folk enjoy the presence of ferocious cave bear pets, faithful ogre flunkies (servants and toadies), bugbear gaolers, and maltreated orcish servant-slaves. An evocative illustration by Trampier reveals what happens to orcish thralls who make mistakes while serving: one who has spilled the giant matron’s stew is about to get walloped in the head with a mighty cast iron skillet, and sent down to the dungeons for special punishment. This is assuming, of course, that the poor sop isn’t killed outright by the blow! 
Some of the treasures hidden within the Steading are quite intriguing as well. The most compelling to my mind is the magic hammer, which is carefully concealed within the giants’ arsenal. The hammer is well hidden, and a magic mouth spell causes misdirection so that it might mislead any snooping adventurers who come to recover it. This appears to be Gary’s winking nod to the parallel incident in Trumpet and also in Thrymskvitha, where the giants steal Mjölnir, the hammer of Thor.
There are deeper mysteries in G1 too. Down in the dungeon beneath the Steading, the adventurers find (likely to their curious surprise) that the stonework is very old and only slightly updated by the giants and their servants from time to time. The implication is that the Steading was built atop a much older evil stronghold of some kind (by the drow?). There is also a vague and ambiguous hint — the ceilings are 20’ and more, and even the tunnel arches are 17’ high at their peaks — that some of these elder evil forces (or their minions) may have been giant foemen as well. 
These ancients worshipped the Elder Elemental God. In the Elder God’s absence (centuries hence) the dungeon level is ruled in Nosnra’s name by “the Keeper,” a horrifying one-eyed hunchback hill giant who rules over the Steading’s slave population with his axe, tortures, and lethal carnivorous apes. His dungeon level is also being excavated and enlarged, which hints that Nosnra and Eclavdra are planning for a significant increase in future power.
The work is being done by giants, but also presumably by dwarven and orcish slaves. Any who dare to disobey the bugbears or the Keeper are first confined, then beaten, and then — if they still will not submit — killed, butchered, and likely eaten.  Many of the orc slaves have escaped from giant tyranny and fled to the east, and while they are trapped there, a grim rebellion is in progress. The orc rebels are in a desperate state however being trapped between the hill giants’ loyal bugbear sentries and a series of natural caverns occupied by carrion crawlers.
Gary’s text and map hint that the “ancient builders of the dungeon” (i.e., the Elder God’s worshippers who discovered these caverns during the temple’s initial rise) deliberately connected their temple complex to the underworld. Even more curious, there are five sinkholes which lead down from the dungeon level to “a series of caves beneath,”  but Gary never detailed the secrets of this deeper nether region.
The most interesting area in the entire dungeon however is the “weird abandoned temple” itself. This area appears to date to Oerth’s Bronze Age. The temple’s stonework is described in such a way — cold, slimy, shifting, and nausea-inducing — that it strongly suggests R’lyeh, and its description further implies that the tentacled Elder Elemental God is partly a Cthulhu-inspired entity. Indeed, staring at the non-Euclidean wall of baroque carvings there will cause any gazer to be seen from afar, and a slimy purple Thing will make contact with such foolish dabblers in a most unnerving way. We learn quite a bit more about this slimy enigma in dungeon module G3, where a greater similar temple of sacrifice is guarded by the drow and the fearful fire giants.
Such fascinating and pulp-infused scenes are found throughout G1, and for that reason its legacy (in some “new school” circles) as merely a simple “dungeon crawl” seems patently unfair. There are surely many, many more secrets buried within Steading’s eight densely-written pages, but someone who delves more cunningly than myself shall be tasked with finding them all. My research work continues, however, and I am studying the rest of Gary’s modules with great enthusiasm. I believe it is quite a testament to G1’s longevity that it still holds so many secrets nearly five decades after its initial publication.
FOOTNOTES TO PART III
 From Jack the Giant Killer, by Joseph Jacobs.
 English Fairy Tales, Retold by Flora Annie Steel, 1918. Refer to Chapter VII, Jack the Giant Killer. This particular Rackham image can be viewed at Project Gutenberg and other sources.
 Dungeon Module G1, Steading of the Hill Giant Chief, by E. Gary Gygax, pg. 2.
 To determine the location of the Steading in relation to the above-ground pond, the reader must refer to the illustration on the back cover of module G1. The curvature of the road and the Steading’s key for room 10A (confirming which map direction is northwest) reveal that the underground stream in the dungeon level flows from southeast to north, as depicted in dungeon encounter areas 22 and 23. This, by the way, and the hex positions of the giant lairs (in the World of Greyhawk) indicate that the realm that is being most heavily assaulted by the giants is likely the Yeomanry, not necessarily Sterich (as featured in GDQ1-7, Queen of the Spiders).
 The Roaring Trumpet, Chapter Six.
 As in English Fairy Tales, Retold by Flora Annie Steel, 1918. Refer again to Chapter VII, Jack the Giant Killer.
 Dungeon Module G1, pg. 2.
 Refer to Gary’s comments made at ENWorld.org on June 21st, 2003 and October 30th, 2005.
 The Roaring Trumpet, Chapter Six.
 For a clearly decipherable version of this tale, refer to Skáldskaparmal, The Poesy of Skalds, as featured in the Gilchrist Brodeur translation of the Prose Edda (see note 13).
 Dungeon Module G1, pg. 5.
 For this architectural quirk refer to Dungeon Module G1, pg. 6.
 Dungeon Module G1, pg. 7.
 Refer to this comment by Gary from October 30th, 2005, which made it clear that this component of G1’s design was deliberate: “I set up the scenario so as to reward stealth and surprise,” he wrote, “[and to] punish the bull-rush.”