I found this little railcar in a collection being sold on FB. The seller had no idea where it came from, and he sold the collection in one lot, but as I had asked he kept this back and sold it to me. I don't have a powered track, so it has to go. $75 includes flat rate box shipping in the lower 48, o.b.o.
Someone who knew what he was doing made up a new brass frame with nicely milled crosspieces for the axles and added a geared motor and whisker wheel pickups. The pickups are nicely insulated from the frame inside a tube from the rear. The gears and universal seem to be Grandt Line O scale products.
Here's a little video of my test on the bench.