The only drakoran head I know that can be made into a trophy is Martley, a level 11 quest. Martley's remains requires a lesser herpetology potion to make it into a trophy.
I believ the only things that can be stuffed are the "remains" of a MOB. I was lucky enought to get the remains of a sprite during an early quest and it now hangs in my Guildhouse...
there are some remains that are quest only items that cannot be made into trophys. and if it just says drakon Head or as such cannot. if you get remains that Taxidermist won't accept check your journal