There are 2 main differences between the generator engine crankshaft and the motorcycle crankshaft. Firstly, the shaft on the drive end of the generator crank doesn't have a register to fit an oil thrower, and secondly, the timing end is a little shorter as it only had one timing gear that drove both the cams and the magneto/governor assembly. To fit the generator crank, you will have to machine down the timing gear retaining nut to a stepped nut to retain the 2 gears. You will also have to play around with the key, as it is a square key on the generator and a woodruff key on the motorcycle. Also, be careful - the generator timing gear looks the same as the camshaft drive gear of the motorcycle, but the keyway is half a tooth out.
Regards,
Eddie.