What Bill may be thinking of is a Miller dynamo that combined a contact breaker, condenser and voltage regulator (yes, the dreaded cartridge). There was also a manual advance facility. I don't know what machines had these units fitted as standard but they were just the job for post-war singles since their dynamos run at engine speed.Thanks Bruce, You have just made me think, I used a Dynamo that has a set of points driven off of it, Some years ago, On my Comet, I think it came off an AJS or something, Must be in the shed ??, I wanted to use my alternator from Time/Trav' but it's another way round a problem, Cheers Bill.
I recall Don Morris had one on his Comet. This allowed him to reduce the rotating items in the Timing Case by two. No need for ATD or Small Idler.