The best way to do this is to get the crank done first, Install an undersize bush in the case and align bore the bush to the proper clearance. BSA used to make bushes of various sizes because most of their dealerships did not have machining capabilities like align boring so they tried to have mix and match parts. Grind the crank to "X" and buy bush "Y". It is best to machine the final bore to the minimum acceptable clearance over the finished, polished crank.

Mr Mike