The simplest and most cost effective answer is to get a P125 or P200 motor (using your old kickstarter quadrant so you can use your original arm). One of my friend's has a few ideas about fitting a P-stator plate to an old bike (GS/SS in his case), but it's going to require a fair bit of fabrication on his part.

Sorry, I hope you get a better answer (where is Mike Hanyi when you need him?)

cheers,
Scott