Phil,
I have heard of owners using them in Mark series engines, but I would suggest you compare them carefully with a set of genuine Mark camwheels - the timing marks may not be in the same position relative to the keyway! I know for a fact that the crankshaft gear looks the same as that on a Mark, but one has the keyway in line with a tooth and the other has the keyway between 2 teeth. There are, however, advantages to using these gears - being from a generator engine produced under a government contract, the materials used were to a higher spec than those used in the motorcycle engine.
Regards,
Eddie.