[Lynn Eades]

O.K. Richard, I dont know much about these three brush generators (dynamo)but I very much doubt that its 12volt.
The more I read the less I think that you can get 12volts out of it.
If you run it, and its not hooked up, it will burn out.
I suggest you find a Lucas unit. The main thing is the mount (drive end bracket) To convert a C39 or C40 from 6 to 12 volts requires the appropriate field coils. The 6 volt armature will work for 12 volt, but the 12volt armature is not up to the job for 6 volts.
Another option is to graft an alternator in if your not too concerned about it looking original. If you go the alt. way, you will probably need a small dia pulley on the alternator.