The replacement of the original Miller dynamo has been a challenge for many Vincent enthusiasts until Alton (http://alton-france.com) introduced its 12v generator designed to fit perfectly in lieu of the original Dynamo. However if you want a reliable and cheap solution, you might want to look at what many did in the 1990s, before the Alton was available. Cheap because you can find a reconditioned generator for only 150 Euros and you will just need some elbow grease to complete the kit. Ken Day – from Australia – did this conversion long ago on his personal bike, and had documented very well all the steps. He sent me his drawings with a note specifying that he was willing to share this information.
Thanks Ken, Philippe
Photo of the installation: