I'm wondering about the number of MOW engines used on the Red, Blue and Orange lines and their make and models.
For the subway, there's one diesel work engine, which can be transferred by road to another line if/when necessary - Plymouth 50-tonner 04443. It's presently based at Cabot Yard on the Red Line but I remember it being based at Wellington on the Orange Line for many years as well.
http://transithistory.org/roster/" onclick="window.open(this.href);return false; has details about it and other work equipment (as well as a full roster of revenue equipment too).