Don't know if this will help or not but one difference I know of with Pre 54 and Post 54 frames was the kickup over the rear wheels was about 2" shorter on the later trucks due to the new flat side beds that were a little deeper.
I traced these on a piece of cardboard to compare when I was thinking about going with a 54 style bed on my 51'.

[img]http://www.chevygmcofkc.org/Gallery/data/3002/1FrameComparison.jpg[/img]

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