The ORER (The Official Railway Equpment Register) reprints, published by the NMRA are an excellent resource. They have the 1943 and 1953 ORERs for sale in the surplus books section of the NMRA member store. I have the 1943 hard cover edition. Its a listing of all rolling stock in interchange service, sorted by railroad and private ownership.
Here is a good online source: http://steamerafreightcars.com/
Modeling the Bellefonte Central Railroad
Fan of the PRR
Garden Railway Enthusiast
Check out my Youtube Channel:
http://www.youtube.com/user/PennsyModeler
This might be a good resource....
https://kalmbachhobbystore.com/products/books/12489__Freight-Cars-of-the-40s-and-50s
Got another one for the forums that is way out of my knowledge base. I volunteer with our local musuem to help with a display in HO scale that another person originally made that gives the impression of the Milwaukee yards here in town during the 1940's and early 50's before the roundhouse was torn down. (I'm the only person the curator could think of to work on it as I had helped with it before. It may not meet the detail specs of some people, but it was intended to give an impression.)
What I would like to do is get proper era cars (and possibly some engines) on that diorama.
From reading some articles, I think that cattle cars would be correct for the era in question, but other than that, given that time frame is not my area of expertise, any help with proper cars (and engines) would be welcomed.