So as fate would have it, a trip to Train Mountain ended up in a pretty much accidental aquirement of a RRSC 173 project. Would it be feasible to machine the included rought RRSC cylinder castings to the Disney diameter? If the only differences in cylinder diameter are internal, it seems like that would be possible.

I suppose it would be possible to bore out the RRSC cylinders to the Disney dimentions if the casting is good enough. RRSC uses a cylinder bushing pressed in place. But I would ask why you would want to do it. Since it is internal, it doesn't effect the look of the engine and the stock RRSC size gives you more than enough power to spin the drivers. The larger cylinders would probably just use more steam.
E-mail me if you are interested and I can point you in the direction of some guys who have built these and have discussed this subject before.
Bill B

The main concern was just power. It'd be nice to be able to pull more than three people, and it'd be nice to be able to take it back to Train Mountain and run there, and there are parts there that have some pretty considerable grades. Thanks for your help.