fido See if you can find a wiring diagram for your model year, this will help detail what bulb and lamp unit was used.
The excellent Brightspark Magnetos website has early Lucas Catalogues and Application data, so is a good place to start.
http: //brightsparkmagnetos.com/ Look in the Library Section.
The literature section of this very forum has links to workshop electrical data, parts lists and illustrations for earlier models.
Swarfy.