Andre covered it. The only 36'/37' cars on my late 40s era layout are wood meat reefers (brine used for lowering temperatures in the car had less effect on wood cars). While hard to tell, I have not seen anything that looked like a 36' boxcar (non-reefer) in pictures from the PW or later time frame. MoW boxcars in the PW era were usually older wood 40' USRA single- or double-sheath cars. If you modeled the 30s and earlier, I could understand you wanting one of the 36’ cars.
FYI-Reefers were used as non-refrigerated boxcars. For example, they were used in the reefer mode to transport fruits and vegetables from the west coast to the east coast, and as boxcars to transport newspapers and magazines from the east coast to the west coast.
