seen a few people swap in gm 4500/5500 axles for the disk brakes and use that hydroboost unit .
as to the 700r4 in this truck
i dont think that trans will live long with that much weight of a truck . better look in to a 4l80-e and
www.usshift.com controller unit. and if you find the 4l80-e from a 3500hd truck from the 90's it will have the parking brake rear tail option also .
the newer axles also open you up to aluminum rims from the same trucks .