The narrow gauge version of those ancient UTLX cars is available from Republic Locomotive Works, so it should be possible, with some bolster and frame work, to make the standard gauge cars.
Pennsy: Somewhere, in the last few days, I saw a company service car made exactly that way. The end domes had been removed, and the holes plated over, but the rivet circles were still there. It may have been a UP car, as I looked at a lot of their tankcars, but I doubt that I could ever find it again.
And here is the "finished", but unlettered, model I started the thread with. It didn't turn out too bad, and still fits within Plate B clearances, so isn't "too big". There may be a prototype somewhere. Platforms and railings are Gold Medal Models beercan tank parts, BLMA trucks, 1025 couplers.