Just looking at a bike for sale which is supposed to be 1944. The frame number seems right (M20 100011), but the engine just has ‘65’ stamped on it. Does anyone know if this is right.
The frame number is too high for a "WM20", by my calculation the last one in service was WM20 122687, have you made a typo?
The Engine number from the factory would have matched the frame, there would have been some new replacement crank cases available unstamped but your "65" could date from any time, is it a period set of cases?