I'm not an extreme authority on this but have the opinion that the crank is essentially 4340 steel forging at a hardness of Rc @ 44. To be good for the bearings it should be at a Rc of 55.

This is a oil hardening steel and to heat treat it will ruin the finish, As it is already to size, this presents a problem.

Maybe someone else has been through this already with a solution such as a hardened sleeve or something?