Back in the 90's I built a very stout XL350 motor using a box full of goodies I bought in the USA. I resisted going big bore and kept it at 350 but used a 12:1 Venolia piston, Megacycle roller cam and springs, ti retainers, Carillo rod, a very nice port job, lightened rockers and CT110 CDI ignition, 36mm Amal MK2. The engine hooted but because I used a non cush drive rear Bultaco wheel I had problems breaking third gear. I was looking into light cush drive hubs and had settled on a small Yamaha hub (can't recall what it was out of) but sold the bike before I bothered.