Reviving this thread as Micro-Trains has among its December 2022 releases an N Scale rendition of this very car, Reading 99048, and with a battleship gun barrel load included (assembly and painting required). 

https://micro-trains.com/index.php?route=product/product&path=63_64&product_id=4690

Sometimes the groups.io search works perfectly, as this citation came right up.  It's probably the first time I've seen Micro-Trains use a photo on Reddit as a reference, but say, ideas can come from anywhere.  Bob, thanks much for posting this.

Now, to try to find some information on Reading 9241, a fifty foot flat car that Micro-Trains is also offering this month as a companion "buffer car."  It's a Reading Class FMc flat built in 1937, looks like part of the series 9200 to 9249 according to the January 1940 ORER.  The image on Reddit does indeed show a flat car coupled to the 99048 but the lettering isn't visible. The fact that "Reading" is a common verb as well as a railroad name should make searches interesting...

George Irwin
Rochester, NY
The Unofficial Micro-Trains Release Report