So, probably this was not originally coach, due to build and size. Unless, as you said Mike that it was significantly altered before it was even brought to Maine.
There were some rumors that parts of coach 17 were helped to make SR&RL Coach #17, but I am not sure if that information is true either. I believe Edaville had both, and they were both lettered 17, and some information on the burned Bridgton Coach and the other 17 coach got mixed together.
But I did see on some older roster of Maine Narrow Gauge stuff and it something about 205 being coach 17, but again, maybe information could have been not true. I made this roster a year or so ago.