89 engine swap

I have a 89 Iroc-z, and just getting out of the military, I have a engine swap coming up. I have a engine in mind, thinkin a t56 tranny swap. I plan on putting a Lt1, then doing the lt4 conversion. sound good? Now to the question, I am not entirly sure what size of rear end to stick in there, but i am fairly sure i do not want to be using my stock rearend. just one more question: what am i getting myself into as far as the auto to manual conversion issues am i looking at? well thanks for any help you can offer.

Jester85