HO injection mold candidates
How about a Pratt trussed single sheathed box car a la B&M and Seaboard?
It could be a stand in for at least half a dozen more cars and shake the box, steam era modelers would want at least one. My guess is maybe one single sheathed car in 6 or 8 had these Pratt trusses so they weren't that uncommon.
If a manufacturer had the capability of switching ends and roofs they could come up with at least half a dozen prototypically correct cars.