Welcome man, check out the article I have in the transmission section about a the 4l80e swap that'll fill you in on that part. Its pretty much a drop in and is really easy especially if you're doing a whole harness and etc for the 6.0. You don't have to change your driveshafts.
SBC to LS motor mounts move the engine back 2 inches putting the whole driveline where it should be. Street and Performance makes a really nice set of mounts I suggest using them.
People don't use the AC compressor because it is a different type. The OBS compressors turn on when you hit the AC button and turn off when you disengage it. The NBS compressors are constant on and use a cycle up/cycle down procedure. I've seen one person use the NBS compressor but he had a bunch of fancy wiring to run it. Most people put a Sanden compressor up on top of the LS swap motor and that will work like a factory OBS system.
So you are saying my 1988 k1500 with a lq9 4l80 will have the drive shafts line up with the proper tcase just have to move cross member back?