Well in mapper there already exist a monkey and human brain we could use that , also, we could use eyes. flesh , radscorp pincers. ears... When i look at it , we already have a lot of stuff we could use.
Imagine this new faction: "The Fore People" based on real life Fore tribe that inhabited Okapa subdistrict of the Eastern Highlands Province of Papua New Guinea they practised post-mortem cannibalism.
Take from wiki: " Upon the death of an individual, the maternal kin were responsible for the dismemberment of the corpse. The women would remove the arms and feet, strip the limbs of muscle, remove the brain and cut open the chest in order to remove internal organs.
Shirley Lindenbaum, one of the early kuru researchers, states that kuru victims were highly regarded as sources of food, because the layer of fat on victims who died quickly resembled pork. Women also were known to feed morsels - such as human brain and various parts of organs - to their children and the elderly."
Of course, this faction is not real tribe they are just some insane people that believe that being cannibal will bring them strength, long life, cure diseases make them immortal and so on
So imagine you go to them you go trough some kind of initiation and do few jobs for them so they see you are loyal , and later they teach you skill how to remove brain from humans without making any damage and you will work for them bringing them brains. Here in play comes the brain we already have in mapper. And same as you learn perk for skining geckos this will be perk to remove brains. And imagine when you become full pledged member they teach you cannibalism so you can eat brains to regains some hp but your intelect drops or something like that.
Also i would inclued that you need some bad dude with karma in big minus to even talk with them. And on other side some other faction will send you to exterminate them if you are good dude
This would like open tons of quest from that faction and later when you become real member
They could look like tribeman from arroyo or they could be some modern sickos in black robes