If you have time you might want to take in the Antique Truck & Engine Museum. It's just across the tracks from the Railway Museum. Their collection includes some Mack trucks used to build Hoover Dam and some HUGE industrial engines.
The last time I visited the Railway Museum the guys in the restoration shop were willing to open all of the access doors on the locomotives so we could have a look at the inner workings. Of special interest is the unusual Fairbanks Morse loco with it's twin crankshaft opposed piston engine.
MTM activities