"Postwar" is tricky; I assume it represents the shift to the later style Dreadnaught ends with straight-tapered main ribs and rectangular top rib, but of course many cars of the 1944 design were built after WW II and what you're identifying as "postwar" AAR cars didn't appear until the 1950s.
I'll admit to not thinking too much about many post WWII cars as my interests fade before 1951... but in my ignorance of 1950-1960 car appearances I always thought of the diagonal panel roof as a major characteristic of what you'd notice that would be a strong indicator that set post war cars apart from pre-8/1945 boxcar construction.
