I've done more with less. I've got a variety pack of mechanisms, including a stock Atlas GP38, which one would assume would be a nominally close fit. I might even have the corpse of the very same Life Like beasty, and see if there's a fit there.
Odds are, the death of your engine is really just a coma, brought on by poorly designed truck pick ups. Resolder a couple of wires, and it might be good to go. It's also pretty easy to install a small decoder in there as well. Despite their chunky details and marginal mechanicals, those old GP's can be made to run pretty smoothly.
Lee