The gaps critical to low rpm running, so maybe there are some gains to be had tinkering with magnet->coil clearance there to be had. I know my cement mixer has the same system and that goes down into the hundreds of rpm when its working against a full (overfilled...) drum of mix, poor thing...
Nick, I just stripped down a old ducati 2stroke off a rotovator (see other thread, making a die filer from a small IC engine

) , and it has a induced coil power mag type ignition like above, except it has the triggering done by points, and a points baseplate and removeable cam which keys to the crank.
Do you want it for post costs? I can saw the magnet out the flywheel easy enough and put it in a box and post it or it can go back to the UK with a relative in someones boot to keep postage down.