Here is an ID plate included in the Wheels and Tracks article. Serial No M14070B Mfd during 8-53. The article also mentions a USAF disposals auction listing in Febr 1956 for Simplex Serial 08195 with engine M16500B mfd in 1954. My brother-in-law once complained that when he wanted a motorcycle during high school, his father bought 3 rough Simplexs at an auction at the airbase in Cheyenne, which he promptly junked. This would have been about 1960. I remember a government surplus auction in Lincoln Nebr which had 2 blue USAF Simplexs, complete and in near running condition. Also NOS engine spare parts, including one crankcase and a few pistons. I bought one box of parts, including a .005 oversize piston.