A fairly late addition to the Nason line of American OO models was their Pennsylvania round roof automobile car. It shows up only in their last (1940) catalog, listed as number 5 in their car list. The listing says “Pennsylvania Round Roof Automobile Car, X-31—Red sides and ends.”
Looking at the bottom, the standard Nason boxcar frame is visible. This car was built up with extra brake details, Scale-Craft trucks, and Kadee couplers. Also, note that the ladders chosen by the builder are standard Scale-Craft ladders.
Finally, looking at the end, I think the builder may have used a different end panel than supplied by Nason. The photo in the 1940 catalog would indicate that the car has a flat panel end. But I can’t tell the maker of the end so it may actually be a Nason part; it is on thinner cardboard stock than the comparable Famoco or Eastern ends, matching the material used on the sides.
and one seen in this article (scroll down), owned by Dick Gresham, has the number 69588. The one in the catalog photo seems to be a different number that ends with a 71. It is possible it is a pre-production model that does not match the production version. The model owned by Dick G. I would note has the flat ends, as seen in the catalog photo.
The model was a first for OO. It filled a niche and was not produced in much quantity I believe. It is one to keep your eyes peeled for if you are looking to own examples of every model in the complete Nason line.