Jim Carter - tech article.
Rear Axle Bumper ChangeError: 1st picture should read 1947 to 1953 instead of 1954 to 1965
More of the same.
Overload Rear BumpersThe 54 frame flattens out over the rear axle to accommodate the deeper bed.
Engineering features (courtesy tclederman)
Cross member changes
Rear Engine motor mounts (courtesy tclederman)
I think you would run into problems if you put a 54 bed on a 47-53 frame. The 54 bed is 3 inches taller.
As oppose to putting a 47-53 bed on a 54 frame, the 54 frame arch at the axle is lower.
Rear axle bump stops on 47-53 frame are mounted under frame arch.
Rear axle bump stops on 54 frame are mounted on side of frame.