If its a 3 speed auto and the trans pan is shaped like texas its a turbo 400, if not its a 350. With the axles not sure, you'd have to look at the ring gear the combo sounds about right they usually have something like that, Gumbos aren't bad in mud not great on the street. With the body lift it might be close, most likely have to trim fenders though. not a chance on the 6" lift clearing 38s, 35s will rub with a 6" if your mean enough. Posi and limited slip are the same thing Posi traction just a brand name and I have an Auburn limited slip and really like it spools wear tires badly. And finally no, driveshaft length should be fine with a 6" lift but you have to grind a little bit off the CV cluster to keep it from binding.