Champion, Eastern/Famoco, Hoffman's, or Nason/Page. Vanden Boom, another firm of mystery, did not list these models.
What I suspect is they may be cars built with Yardmaster sides, a firm I look at here. I have yet to see a boxed example of any kit by this firm, but as I have mentioned elsewhere in this site there were Yardmaster kits listed in lots sold at the Morlok auction and I strongly suspect there are a few of them out there. And they certainly listed car sides of the type seen on these cars in their advertising.
The Armour car is beautifully built up but I think fairly recently. The FGEX car is a bit rougher and was not completed by the original builder. It is on a Picard body with a Nason frame and trucks, and is a model I plan to (with time) bring more to completion.
Curiously and probably significantly there is a “W” code found on these sides. Others have speculated that when that this W is present the sides were actually made by Westbrook. The FGEX car is W-3 and the Armour car W-16. Westbrook definitely made OO parts for other companies (wood parts and sides), certainly for Eastern/Famoco and very likely also for Nason. These sides of mystery look generally similar to sides from those lines for sure but are not actually the sides they sold.
Perhaps somewhere in the bowels of your collection you have some Yardmaster kits and can solve this mystery. And, if nothing else, perhaps this post will inspire a few readers to sort out their vintage models with printed sides by brand of side as I have, it is an interesting project.