That is a common problem on big blocks but all my steel 340 cranks are drilled for the correct size pilot( the larger one). The easy fix is to use the later model one that comes in the new pickups. The fit in the back of the crank hub where the convertor hub goes. Don't get the ones with needle bearing but the one with the bushing.
Mopar created a big problem when they rough drilled the cranks for auto tranny and only finish drilled the ones for a std tranny.