If the 302 is going into a GMC, its a bolt in.You can use a 48-53 Chevy or GMC bellhousing which will bolt up on your stock crossmember using 48-53 rear mounts.What are you going to do with your pedals?as they originaly mounted to the 45 clutch housing.I modifed the later housing, other guys have made brackets, perhaps you have converted to swing pedals? if you are using a big hunker for a damper pulley, it may foul the radiator.
If you front axle is in good shape, the beam axle can be made to work well, but you won't be able to lower it more than a few inches.I like the classic hot rod look of a traditional beam front axle, but its your truck.