74 Scamp pain

Sorry guys my measurement was center to center, it's 4.5:oops: I swear this is my third a-body and I still don't know enough. Some of the cast #'s on the drum are 80988-11 ,987 ,55722. my guess is one is a lot # the one with the -11 may tell me more if I had some kind of good cross referance, I think that I need a Motors manual. I'm guessing it is an 81/4 with 2.45 gears since the tag off the rear says 2.45 4 19 4