After discussing the history of the Motorshop frames with Chopper Dave and Irish Rich a couple of weeks back. We think my frame has the straight tube under the seat to accommodate the taller Shovelhead motors. Rich also said that since they only made around 300 that mine would probably be a later frame with M.S.286 stamped on it. Dave also said they were made in 1970 and 1971 give or take. If anybody has any more knowledge on the frames or the makers let me know.