I didn't read but the first 2 or 3 posts but before I forget here let me throw in something I saw on TV the other day. I was watching that new show on Spike TV called Extreme 4X4, now if you can, they put the reruns on all the time. Try watching them because in their CJ jeep build they do they show and explain how to regear a rear end, etc and explain just what Mike said to do about using the old rings or shims shall i say, etc. It helped me under stand a lot more on rear ends until about half way through it they lost me because I was still trying to think of the earlier stuff they did (I am slow and forget real fast). Oh and no I am not old hehe.
But yeah try looking for that episode, they cast it a lot on TV and it should help you heaps.

Good luck!