Jason,
I am interested to hear that a B&SR flat car still exists. The B&SR had 44 of them starting in 1882 at Laconia Car Company going down to 2 at Portland Company in 1913 according to the roster in Two Feet To The Lakes. I doubt many of them made it down to Edaville RR in 1945 and those were mostly used for parts to built the Edaville excursion cars.
My Edaville Railroad book by Linwood Moody in 1947 only lists 14 flat cars in 1947.
I keep up with everything that was on the Edaville Roster; which small Diesel is going to go to Maine Machine Works next store?
Ted Miles, fan of all things Maine Narrow Gauge