I could be mistaken but, I don't believe any Postwar period ever mentioned "size" in their descriptions. Another words, I don't ever remember seeing a catalog from the 1950's described a "40' " boxcar. It would simply be listed as a boxcar. About the only descriptive difference I remember was a "Double Door" box car. But still no mention of 40', 50' or whatever. With the exception of Atlas and Weaver, Descriptives probably didn't start until perhaps the 1980"s?
So, as mentioned previous, there were no standards for manufacturers to follow. I betcha a 40' boxcar from Lionel, MTH, Weaver, Williams, and K-line all put side by side would have differences in length, width, height.
So for a new guy who is looking for some sort of consistency could get flustered rather quickly.
Look for 1/48 scale on the description, that should help.
