I picked up a collection with the below gondola in it. There are no markings on it as I think it has been repainted at least once. I've tried comparing it to photos of prewar Marx, Lionel, and American Flyer. The couplers seem to be similar to Lionel latch couplers. The strangest part is the mounting of the wheels. It looks like a second set of wheels could go in the extra holes but I don't think they would fit.
I still find it fascinating what turns up in these old collections. After 30+ years of buying many collections, unusual items or items I've never seen still pop up.