which 833 for a body ?

I don't understand this. "Not a lot of factory 833's gonna fit this application...."

Any A body or F body 833 is a bolt in swap. The 76 only cast iron OD, although rare, will hold up well behind a moderate big block. A body 833s are not very difficult to find. Even the early ball and trunion units should be considered. They are arguably a little stronger.