You should take another look at the 70 truck with a 283 in it. It could be a 307 or possibly a 350. Not that there is anything wrong with any of these engines but it's not likely that a 70 has a 283. There were a number of changes such as the mount holes in the heads which attach alternator brackets, PS pump, etc., which the 283 did not have.
If you stay with the standard trans you will need a V-8 bellhousing and flywheel. As 3B states you will need the side mount and rear mount crossmembers if you use the auto trans. Also a cooler or a new radiator set up for an auto trans. Factor in other items such as exhaust, trans shifter, and possibly a drive shaft.
Fred
