Kurt Laughlin wrote:

As best as I can tell, there were four main types: 1937, 1937 (modified), 1944, and postwar. What distinguishes theses from each other?

This isn't a simple question, Kurt, and I don't think you can answer it with dimensions alone. Various buyers chose their own interior height, in particular, and so cars otherwise meeting, for example the original 1937 design, could vary a fair amount in dimensions. The 1944 design really isn't different from the prewar cars except that the "Improved Dreadnaught" end was shown. In October, 1947, the AAR drawings changed to 10 ft. 6 in. inside height, but not all roads were buying cars with that size.
I think you can do better by looking at features visible in photographs. But someone who has spent a lot of time with these cars, such as Ed Hawkins or Richard Hendrickson, may feel that there are also characteristic or "signature" dimensions. If so, I'd like to hear about it.

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