The race alternator kits that Durbahn.de sell are based around Ducati ST3?4? alternators - they're an aluminium hub with rare earth magnets in it - 75mm diameter, ~20mm wide, with the coils run around them (Bevel Ducati guys use them as a bolt in upgrade in their old shitters). There's enough room before you hit magnets to bore them out big enough to slide over the hub of the small crank GSX alternator, and clamp them with a stepped washer under the crank nut. would be the absolute lightest alternator you could run, very narrow too. Converting to a modern sprag clutch is interesting - I was just looking at the item out of a SV650 wondering if it could be used...