Many thanks to all, especially to Ian who has been a great help, I believe his ID is 100%, and emailed the following info which others may be able to use: "Hi Al, the frame you have is an OC600 very close to mine. The motor you need is the same - the correct serial number should start with an ED but worst case you could use from another similar bike. Gearbox should be TG."
Anybody have an OC600 engine and trans for sale? also wheels?
Thanks again to all.
Al