I just found out something: Any of those quest items can be sold from the "Equipped" items bag IF you can equip them. I just sold Arben's Sword, Talos' Axe and Hermosa's Necklace. They all went for zero (0) gold each but, they're out of my inventory and I cannot "accidentally" enchant them. cheer

I'd like to close by quoting Bellegar's famous last rhyme:

"Cursed be the mother that bred thee!
The wench must have been a hell-spawned banshee!"