Sorry to hear about your woes GB . . . but good luck, sounds as if you're all over it already.
On the belt thing, I have the same kit as Morris (and DVR2 running at 12). Haven't thought about it since fitting it a couple of years back. Which means I like it!
Probably is a bit quieter but it's a long time since I had a chain on there 'cos prior to the Dyn Reg Mike kit, I had the SRM one. (Which I did manage to kill in the end.)
Does it knacker the dynamo turning it faster? Don't think so - my dyn has lasted over 10 years without major surgery, and dunno how long it had been running before I got my hands on it. That's longer than any other dynamo on other bikes hereabouts, and I think is pretty darn good. (Mind you, I'm not doing Musky Revs!) It'll now fail, natch.
One point worth bearing in mind: You might find you have to ease off a little bit of alloy on the inner timing case 'compartment wall' to get pulley clearance: some castings are a bit fatter than others. I had to shave a bit off when fitting the first kit, to get the drive pulley on with adequate clearance and I believe some other people have had to do the same. But only talking a gnat's cock's worth and a dremel. (So, yes, an insect was seriously mutilated in the course of doing the mod, so I apologise to any outraged #metoo entomologists.)
But I guess the key Q is - Is it actually worth it for a 6v system, which will be quite fine as it was designed??