Question about various rear ends

Stepper, I'll take the time for ya buddy. Crate covered it for ya pretty good. Ill share my knowledge as that's what this site is about. By the way, WELCOME.
Early model 8.75's up till about 72 would have been small bolt pattern. In 73 they could have been either due to the fact that was the year they made the change. To determine which one you are looking at, place your tape over one stud and pull it diagonally to the oposing stud. It will either measure 4" or 4.5" to the center of the next one.
On the case issue. Some will debate the issue of which is stronger. The 489 case does have the largest dia. pinion shaft at 1.75". When ordering any parts you will need to specify which one your working with. The guts are different. I'm partial to the 489 case and wont argue with others about which is better. Keep this in mind. The bolts on the ring gear are left handed and most generally will have been locktited. You should do the same when you reassemble the unit. Depending on what kinda power you'll be putting to it will depend on needs. Ma Mopar felt that an 8.75 was adequate for use behind an automatic Hemi 68 SS Dart. 4 speeds got the Dana 60. Perches will all be located in the same spot for all of em. Let us know if ya need anymore help.
Small Block