The magneto setup you have is a Miller ignition as youv'e already discovered, which were used on other engines including British Anzani Pilots, and you should be able to get hold of one for not much money ( the Pilot is in fact quite a nice motor for small boats, but isn't popular for some reason, and therefore cheap!)
These Anzanis had the Miller ignition for quite a while, and went to Wico ignitions later, but they are interchangeable as a flywheel and baseplate set.
I'll have a rummage through my Anzani bits, but don't think at the moment that I will have any of the parts you need.
Points gap 0.020" - fuel mix for your Ferrier probably 16:1 which won't hurt it. Rick.