AAR Steel Boxcar Question


I have noticed that a number of early 1937 AAR boxcars were built with lapped seams and the later cars were done with "crimped seams". I am working on a couple of SP 1937 AAR cars and there appears to be a transition from the B-50-18 to the B-50-19. It is hard to tell from photos when the transition occurred or if it was specific to a builder. I noticed that some of the 50' SP cars appeared to be of lapped construction.
Has anyone done any research on this subject?
This detail is noticeble on my 1/4" scale models and would like to be correct in choosing the proper Intermountain body for a project.

Gene Deimling
Los Gatos, CA

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