I would also vote for a Williams engine, but you might consider some of the Lionel post-war locomotives. They were tanks and many of them are still running some 50-60 years later. I know that the Carnegie Science Center layout in Pittsburgh was running a number of post-war Lionel engines almost continuously. Choo-Choo Barn does the same, I think.
Lock them in forward, set the handles appropriately, and watch 'em run.
George