Figured I'd post some facts and data here on this quest since there seems to be a lot speculation and nothing written in stone.
1) Yes, the White Dragon Helm can be turned in for the Clawed Griffin Sword, which can be turned in for the White Dragonscale Boots. I can confirm this as of 7:30am July 30th, 2003 as I did it this morning.
2) You only need mid to high Amiable faction to do the turn-in. You don't need even close to max Ally. Lord Yelinak was indifferent to me this morning when I conned him, I used Collaboration (I'm an Enchanter, raises faction by 300), and he was Amiable and responded to me allowing me to do the turn-in. From what I understand, Indifferent faction range is 0 to 99, and Amiable is 100 to 499. So with Collaboration, I had between 300 and 399, which puts my faction range in mid to high Amiable range.
3) As someone else posted, if Yelinak doesn't respond to you, you're not standing in the correct place. You need to be standing under him, pretty much in his stomach to get the hail response. If you're in the correct place, you will *always* get a response of some sort. If your faction isn't high enough, he'll call you talking refuse or some other form of insult, if your faction is high enough, he'll talk and give you the quest.
As for gaining Yelinak faction, a few tips. I'm in a big guild, but not an uber raiding guild. I purchased my White Dragon Helm in the Bazaar. I've never gotten a faction hit from King Tormax. I was actually at max KOS to Yelinak when I started my faction work. I turned in approximately 300 to 400 Giant Warrior Helmets, Frost Giant Toes, and Storm Giant Toes to Lieutenant Milven. I did the Kromzek Mercenary Broaches quest about 60 to 80 times. I did the Kromzek Mercenary Captains Broach quest twice. I did the Liason/Eysa messenger quest about 30 to 40 times. I did the Cobalt Scar key once, which contrary to the quest listing, does *not* give any sort of faction hit at all. And lastly, I was part of a group that cleared King Tormax's throne room and all his guards once, so I got about five faction hits there, but none from Tormax himself. All of that brought me to Indifferent. So if you're not an Enchanter, you'll have to do a little bit more work. :)
Hope this is of some help to those working on this quest.