My best friend just put 36 12.50 16.5 on his 79 shortbed. No lift stock 3/4 ton suspension. He cut the front fenders and they look mean. Everything that was removed can be hidden under fender flares. That much tire in stock wheelwell is impressive.
You don't know until you try, but i can help you out if you decide that you want to put a certain size under that beast. Its all about how you want it to look and how much your willing to do/ spend.