conversion is fairly simple stator should have 3 wires
white/green, green/black and green/yellow.
connect green/blackand green/yellow together
then wire bike as 12volt using zener rectifier or solid state parts. Be sure to change bulbs to 12volt
Working from memory on this one.
If I'm wrong someone will correct me
Yep, that will do it just fine. Don't junk the 6v horn though, keep it and feed it 12v. Now that's what I call LOUD.
It will last for years as it is only used rarely.
Roy.