First, let's clarify the mu thing. Back in the "olden" days of diesel engines, railroads had the option of ordering engines with or without mu capabilities. Of course, most road engines were ordered with, for obvious reasons. When it came to switch engines, it was available at the railroads request. Some smaller roads probably opted not to have it on their switchers possibly for the added cost, or they may have not found the need for it. That being said, as far as I know, the GTW SW switcher series were either ordered with mu capabilities, or added on after the fact. I don't know about some of their Alco switchers, but I think most of them had mu also. A real nice book to have is Grand Trunk Railway in Color, volume #1...lots of pictures of first generation GTW diesels in the Green and Vermillion colors.