If you want to go 4l80 (or 4l85 whatever) you will need a W x-member and a North west fabs 6 bolt adapter for your tcase. I have been told that you can use the original 4l80E T-case adapter but I have yet to have the pieces in my shop to test the waters. (It's a WIP) It's commonly known if you are having a hard time finding a 4wd 4l80e for cheap you can get a 2wd unit out of certain years of 2500 work vans that had a 6.0 in them, it just takes plugging a lube hole and then shortening the shaft (I recomend using precision tools to measure and cut once rather than internet booshwa). You can tell it is the right unit if it has the 32 splines all the way from the beginning to the inner seal (meaning you have to take off the tailshaft housing to eyeball it and some people freak out about you doing that to their for sell unit.
As previously mentioned you need either a stand-alone controller or a LS PCM to control it, and short of doing the LS swap (which is what I have going on) I am not familiar with using the LS PCM on an older TBI truck but I am aware it has been done with some degree of success.
