First question Pete, is your bike definitely 1939 ? if so you need a unique one year only number plate. Adrie degraff had made some don't know if he has any left . This number plate also has a unique light which Alan Moore has put a good article on this forum about how to convert a car one to a motorcycle one as when they are rarely available they command high prices. The plate you have is not Ariel as it should have an embossed line across the centre. I have both the plate and light and will try and post a picture to help.