No, they won't MU with each other... in fact, I don't think the Model 40 can MU with anything, and the RS12, if I'm right, can only MU with another Baldwin... but still they are the two operational units at Travel Town. When there is a need to move around equipment at the land locked museum, one of these two engines is fired up. The Model 40 is missing one of its prime movers, while the RS12 is basically intact.