I recently bought an LS 6.0 and 4L60E transmission. I got a pretty good deal and wasn't thrilled about rebuilding the old 350 and having a TH350 3spd auto. It will need some parts that were removed, and the trans is for a 2WD so I ordered a 4x4 adapter and tailshaft. I won't document the process, since I found a very good video online that I can't top.
https://www.youtube.com/watch?v=4IDfs0UMne0 I'll be using this video as a guide to make sure I get it right.