It could be a standard taper,why dont you measure it.In my experience engines with short drive shafts are often industrial.JAP for instance made 100 times more industrial engines than actual bike engines.To mount one with a bike gearbox,you often need to offset it somewhat to that side,to line up the chain.Dont go for an excessive overhang,as likely the shaft will fracture at the keyway.Any one with a lathe will be able to cut an accurate taper in a sprocket blank,and as has been suggested the sprocket can be rebanded.The key will probably be a modified Woodruffe key[cut short and reduced in height,to avoid weakening the engine mainshaft.]Nortons and JAPs both use tapered keyed sprockets,but different sized shafts.Regards John.
