Hi All,
I would think that the most likely cause is misalignment??
The oil pump is not a good fit on its studs and can be moved about to some degree
When fitting the pump lift it towards the crank worm, BUT make sure theres a little play in the engagement of the pump gear and crank
Trial fit the rev drive with its housing, the screw holes in this are somewhat oversize, check that it seats flat against the casing and then turn over the engine several times to check theres no tight spot
The only other thought I have is ,
Was the gear that broke original or aftermarket?? Maybe overhardened ????
HTH
John O R