See the link below to Bruce Heald's book below, if it doesn't work search "Uncle Sam II Lake Winnipesaukee". Basically this states that it was a converted PT boat, 72 x 20 trucked to the lake for use as the mail boat. Top speed is listed at 15 knots which would seem to indicate a change of power plant. I know we have an old copy of "Follow the Mount" somewhere, I believe this is a passage from that book.
https://books.google.com/books?id=ZR...saukee&f=false