This is WAAAAAY outta my league, so was trying to stay out of it- but dis'arvo after a hard days slog in the sun, I ran into a work buddy who has a '73 Tr-tr-tri- *conf2*tri-...Tryhard as I can can't say it ..and had a yarn with .anyway he said 'it' has a boyer (dunno what series/model) and would only run on one side.
He said it had the original 12V coils, after some messing 'round, he went and bought some 6V coils and voila (yea know that Italian word when good fun stuff happens- not the instrument) ....seems something to do with being/not in series, buggered things..maybe not relevant here, but figured I'd pass it on anyway while it's fresh in my brain. I'll harass him more next time- hope it's helpfull