I had just looked through those pics prior to posting. I need to get more sleep at night!
Yeah, that looks like an 8 3/4". Are you positive it's not an original 57 rear though? They were chunk type also but weren't real strong. I haven't looked at one of those in a long time.
If it is a Mopar rear, the chunk will have one of two casting numbers on it-489 or 762. I don't remember which one is the stronger of the two but either is better than the OG rearend.