i think in the orignal sculpt the likeness is there, just need to thicken him up, change a bit his eyes (especially at the end they need to be more down and not that high) and tweaking the chin, making it bigger, longer and fat and like uscmhicks making the neck much more thicker then before. the overall shape of the head should be refined, you can also see at the top of the head, where the hair is, how we modified it. i've tried to mix these things together, what uscmhicks showed us combined with the likeness of rainman and some of my suggestions:
left my interpretation, middle rainman, right uscmhicks