With a flatbed where clearance is no problem, I would find a frame cutoff from a one ton cab and chassis. I would splice the two frames right behind the cab. The reason I would look for a cab and chassis is because dually pickups have a 10" winder rear. It doesn't particularly have to be a Chev. Your wheels aren't going to match the front at any way you go. I would install a brake proportioning valve. A newer rear will have better brakes and they will lock up on slick pavement.