My chainsaw 2 theory
 

i think Nubbins is the dead hitchhiker and i think Chop top is his twin cuz the mark on thier face and why he treats him like a live human being and look at the thing around his neck plus theres a scene that was deleted where there drivng a meat truck and there sewing his head together from the gun shot and the cook says "see what happens when your bring your brother with you"

I've never quite adequately figured out who Choptop is, or where he came from. I've heard theories that he was a Vietnam vet(but I also heard that about the character in the 1st one) brother who returned home(or possibly got booted out of the military for some perpatrated weirdness). I don't remember any lines in the film to suggest where he came from. The original guy got squashed pretty good. I would think it would require more than a plate in his skull to repair him.