help identify this 8.75

The large castellated nuts on the end of the brake drum are a dead giveaway that it was used up through 64 and probably on a B Body. You need a brake drum puller to remove the brake drum (PITA). I'm on the 62 to 65 Mopar forum (98% B Body)and quite a few people there ditch these rear ends for a 65 - 70 B Body 8.75 for ease of maintenance. Can't answer your other questions.