Eliminating Battery,Installing Magneto.

Shotgun:
I have never found a 6V regulator that has a fast enough reaction time to work without a battery for any length of time. However if you change to a 12V generator the regulator and capacitor (Harley parts books call it a horn capacitor but it realy is to protect the regulator) for a late 50s XLCH without battery will cure your problems. Except that some states require the headlight and tail light to stay on for 3 minutes with out the engine runing to get a safety sticker. I used to tie a battery on with a bungee cord long enough to get inspected.
Dusty

Shotgun:
I don' remember for sure seems like the top of the shaft was different on tach cable mags.
If the capacitor isn't avialble anymore you can measure one ( seems like the value was stamped on the end )and get a subtute from most any electronics supply. Same with the regulator I used to buy them from a Bosh wholesaler for about half of what Hardly wanted. But you will have to find someone that has one to get the number as I can't find the note book that had the number.
Dusty