I have a -68 Spitfire with Boyer Mk3 ignition. Guess its quite old, because the magic box has a black label on it, not white as on the ones for sale now.
It's an easy starter provided that the battery is fully charged so that not really a problem. I have read that the MkIV is not that voltage sensitive and is "better" in some ways.
And I guess that I can just replace the magic box and keep the magnets and the pickups?
So is it worthwhile? Also thinking of converting it back to points ignition.
I feel that the bike is a bit "lazy" on acceleration, but that may be a carburetter problem (Mikuni VM32). The Mikunis will be replaced with new Amals during winter.
I have a new MK IV on my Thunderbolt, very easy to fit and I used their dual coil as well. Lovely spark !