I see you just joined. I believe what you want is all the benefits of a newer chassis and engine without the emissions testing and government intrusion factors. If you did find a body, it would be the part with a title. You do not state what State you live in, or anything else on your profile. Best bets would to buy a salvage or wrecked late model, and a used older truck. Then, if you are handy with tools start by taking both bodies off and grab your tape measure. I would pay particular attention that the wheelbase of both trucks is the same, but many customisers cut the rear frames to "c" them to accomidate extreme lowering, so you could change the wheelbases. I sense frustration with the system, and you are trying to go around it. Good luck.