Well so far everybody on here has hit the nail on the head. And given where he came from the whole 9 yards as you put it, he definately should not be housed with another snake, he is being stressed even more in my opinion by being housed with another snake. Even though you guys have nursed him back to health and he is doing much better, in the wild even though he isn't in the wild he is still an animal and they aren't those cuddly they wanna snuggle animals. They go by instinct and his instinct from being starved and suffering from the previous owner and now living with another snake may be a little too much for him to handle and that may be why he is showing this aggression. Unfortunately because of his previous situation it is probably best for him to live by himself, its also honestly not a great idea to house multiple snakes. Especially a snake that came from such conditions he may be harboring underlying ailments that because he is being housed with another snake he will pass to the other.

I hope this helps, good luck!

BTW I own 11 snakes and out of the 11 (4) were rescues and 2 of them had underlying conditions that had I housed them all together would have had a devastating effect on my entire population :{