Tim, I was referring to the rear cross-sill to frame location in reference to that 50 inch bed width. Like you said, the bed inside width was the same for all AD pickups.
The 1/2 tons with wider frame at the rear would have the rear cross sill mounting points farther apart to match the frame width, and the 3/4 tons with narrower frame would have a different rear cross sill with narrow spaced mounting points. The frame difference was about a foot, which would put the 3/4 ton bed mounting bolts about 6 inches farther inboard on each side.
