The Fleischmann models pictured on page 41 were created by the US military after World War Two when the planners "knew" the next big war would be in Europe. There were 5 kit cars in the series. In addition to the low- and high-side gondolas and box car shown there was a flat car and a tank car. The flat car was merely the floor of the gondolas or box car without any sides, ends, etc. The design was such that the cars could be assembled in-theater with troop or indigenous (unskilled) labor. The expectation was that trucks and couplers would be scrounged in-theater. I have an Army manual with plans and assembly instructions.
I submitted an article to RMC on the tank car kit but it was never published. My material is being returned to me. The point of the article was mainly that flat cars (the P2K model) were loaded in 1953, moved hither, thither and yon but not unloaded until the early 1980s. Sort of solves the empty/load in open top cars conundrum in at least one instance.
I was stationed in Germany for 3 tours and spent every off-duty chance I could photographing railroad subjects. I came across former US freight cars occasionally but never any of the kit cars nor the 2-dome tank car to the best of my recollection.
Out in the Badlands of New Mexico