[Woodz428]

Between the 2 you mentioned, it's easy. The 9" has a removable carrier so gear changes can be done on a bench. The 8.8 has an intregal carrier and the gears come out a cover on the back. There was also an 8" used in many 60's and 70s cars, it looks like a small 9" and has more ribbing (at least the later 8" ones do). Rotating the pinion and counting how may rotations occurs with the axle is the simplest way to check ratio, if it is open(non-posi) one flange will have to be held.