Hey D, how's it goin'? I have heard that apparently, they kept the same basic bed design on GM trucks from 1954 all the way to 1987 (last of the "real" stepsides). The only difference I could see is that the '54-'55 1st series bed has the shape of the fenders "embossed" into the side of the bed, while the newer trucks use a flat bedside. Is it the correct thing to do? No, but if you aren't doing a 100 point resto, who cares? It's your truck, anyway! I had thought of just this same thing, as AD trucks up here in Ontario don't seem to survive with their original beds. I would suggest hunting down an original '54 or '55 1st series and inspecting/measuring the bed mounting points-this will allow you to approximate the stock height when you fabricate the new mounts for yours. Good luck-let us know how it works out.
Wannabe
