The center of the 2003 frame drops down farther than a 67-72 frame. If you put a 67-72 body on a newer frame, the cab would sit alot lower than the bed. This is the problem with doing what I'm doing.
My fix was removing the crossmembers from the bottum of the bed. This would drop the bed to the frame by about 3.5 inches. The cab will sit 5 inches above the frame, which sounds like a lot but if you look at a 2000's 2500HD truck about the same amount of frame is showing.
Your not going to see through to the other side.