Caught one of these at Cookson siding on the old MP (southeast of Wagoner,OK) a few years ago. One of the hood doors was open, and when I looked inside there was nothing. Obviously you expected the prime mover to be removed, but not even any weight. Not sure if this was a radio control unit, since it didn't seem to look much like a slug.
No traction motors or fuel tank. This site says that reportedly, their prime movers are still in place. However if you did not see one then they must be gone too.