Hithere is a 1937 hand change ,panel tank M20 on Marktplaats.The translation is not very good .There may be the answers to a few recent posts here,(measurement of the indicator hole and number plate position). This link may get you there,
if not search Marktplaats for Bsa M20.

http://www.marktplaats.nl/a/motoren/motoren-oldtimers/m696413390-bsa-m-20-1937-hand-schakeling-zeer-zeldzaam.html?c=8c285449651fa109c354bbabe740c1b&previousPage=lr
cheers Rick

email (option): richardholt@rocketmail.com