Was recently looking at this myself, but it seems to be a LOT of work/expense. A beefed up 4l60e seems to be the better option IMHO. This link is right in the stickies and may have the info you're looking for.
http://www.impalassforum.com/vBulle...stickied-4l80e-swap-questions-wiring-etc.html
http://www.impalassforum.com/vBulle...stickied-4l80e-swap-questions-wiring-etc.html