treegrower - You can save the research on the rear frame width measurement at least on your discovered '53 or older frame.
According to the
GM Heritage Vehicle Information Kit files, all AD series 1/2 tons from 1947-55.1 1st Series trucks use the same rear frame width measurement as I posted above for the '54.
You might consider looking at an adjustable width bolt in tow hitch, something like this
CURT C13702 from etrailer as a possible option for a pre-built unit.
