Well, keep the mag anyway Beast! Great decision! Some electronickery is darn useful and I suspect you have some already . . .
Re the dynamo saying '6volt' - it will say that because they all were, originally. Thing is, they can be converted to operate at 12volt by changing the regulator, and in some cases making some simple changes to the internal wiring of the dynamo's field coil and brushes to suit the way the regulator works. An E3L dynamo is quite capable of producing enough to keep a 12v system charged up. What comes out of the D terminal depends on what is fed into it at the F(ield coil) terminal. The regulator sees to it that what goes into F is what's required to deliver enough output from D to support the immediate load on the battery. The associated 'cut-out' makes sure nothing goes into F when the engine's stopped or the revs are so low that the dynamo is producing less voltage than the battery already has. If that wasn't there, the battery would try to drive the dynamo like a little electric motor. Which it could on the bench, but not when connected to all 650cc's of BSA's finest. So the dynamo would get hot, maybe fry, and the bike too maybe. Gulp.
Some solid state regulators/cut-outs seem to require a handful of throttle to get them to start up, others are better. I've had both. But no matter - you've got a system, and it works . . . . if it ain't broke, etc.
Re changing points and condensers at the side of the road . . . Have No Fear. Seriously. The points gap will need a minor adjustment/clean now and again, and very occasionally the HT pick-ups at the bottom of the plug leads need a bit of tlc. But they really are extremely reliable and require little more than that, absent some other problem. If you're in doubt as the state of your mag, see other threads here on getting them fixed - there are several good people out there who can sort you out at reasonable prices - less, certainly, than any of the electronic options. A good one will last for years and years with just routine care. Tired ones often work even when they're in extremis. They're amazing things.
Having said that, I would say that if you have the standard Gold Flash set-up with the Automatic Timing Device, so-called, to control the advance and retard of the spark, it is worth closely inspecting the fibre pinion that turns the magneto and carries this device. Every time you have the outer timing cover off. The pinions do wear, and eventually the teeth can wear down to nothing, like the incisors on an old dog. . . . Roadside tinkering won't help then, and there's no way home apart from buying a bus ticket. Except it's the middle of the night, raining of course as you say, and bus services were probably abolished when Noah was an apprentice boat-builder.
