Length of the rear end?

So it didn't matter what engine was in the vehicle at all. The entire rear was the same depending on the year? That's quite interesting.

I'm obviously not as educated about the rear as I am other parts of the car. So I understand what the rear end is, but I thought it was all one part. It's not?

There several parts to a rearend but the size refers to the ring gear ie 7.25" has a 7.25" ring gear 8.25 has an 8.25" ring gear etc the axles come in both small and large bolt patterns for you wheels. Tell us what you're trying to accomplish and we can give you some suggestions on rearends