Not matching engine and frame numbers, frame originally had a B34 engine, but has had a change at sometime, with a similar type of the same era, frame has been in a bump at sometime, and the engine that was in it has some small damage at the rear of the cases, as shown, the engine appears seized from standing and has some damage to the exhaust port area. As you can see there are remains of the original rear flat type competition mudguard which has been cut down!
Very rare model when restored, recently imported from the USA, comes with USA title and NOVA for ease of restoration.
Info from the BSAOC:- "The frame is ZB34A alloy plunger supplied to Rich Child USA on the 15th April 1951. The engine went to Rich Child in the USA East Coast on 13 January 1950."