I had been wanting to build a Pacific Rail Shops kit. I kept a diligent eye on eBay and eventually found and won this 1937 AAR box car kit. Mine did not come in the original box, did not include instructions, and had no trucks. It was just the kit parts. The parts were all new, so no problems there. After some research, I decided that the PRR X37 box car class came closest to this model, as far as Pennsy cars was concerned, so that is what I set out to build. It is not an exact match. It is my understanding that the PRR, "The Standard Railroad of the World", made its own version of this standard box car design. Upon further inspection, I concluded the differences were rather subtle. Both the kit and the prototype body have the rounded corners, so that is a match. I have not seen any prototype photos of the PRR's X37 roof, so I cannot comment on it. The car's sides seem to be spot-on. However, the side sills on the PRR version ran to past the small protrusion under the side. I discovered that too late to make the change on my model.
However, I later noticed that the door stop "triangle" should be moved further to the right as well. This would have been more work than I would have been willing to do anyway. The ends of the model are very close. The model has 4/5 dreadnaught ends, whereas the PRR X37 class had 5/5 dreadnaughts. However, the model's 9 ribs appear to be in the correct location and with the matching spacing. It is just that the model doesn't have the top one. I decided that I can live with that difference. Some other minor differences are mentioned in the construction article.