There are a few choices out there Dev, but I guess one at the more affordable end of the spectrum is the Thorspark kit from
https://www.sussexmotorcycles.com/Seen a few of them working fine, but have also heard gripes from people who find them hard to set up, and there are reports of misfiring. No idea as to the merits of the gripes, however. Available in 6v as well as 12v.
Thorspark systems retain the magneto's advance and retard ; most (or all?) others have programmed-in curves.
Some systems require more power than others, but they all need an external supply. So in whatever case you'd need to know the dynamo and regulator were up for it.
Pazon has a very good name, but I don't have any experience so can't comment.
All require an external coil or coils putting somewhere discreet; the magneto's HT leads become redundant (but can be retained, going nowhere, for the 'look').
I think all of them use a wasted spark system on 360° twins - so both plugs fire at once. An advantage, as the potential problem of an uneven firing interval is eliminated.
I think you need to strobe them all too, to set them up - which is a good thing but nonetheless not everyone's favourite where it involves removing the primary chaincase for proper access to the crank.
I've had Boyer Bransden kit on 2 bikes. It was OK - but they were both alternator machines. I've not personally had any other electronic ignition system on classic bikes.
Would I go there in your shoes rather than sort the magneto?
Don't think I would for an early A7 to be honest. It's probably even-stevens in terms of money by the time you're done, and if I had a nice 1949 bike like that I'd want to keep it original I think, although I would conceal a decent modern voltage regulator in the old Lucas box, regardless.
