On an internally balanced engine it is OK to make a new key way 180 degrees from the factory one in both the dampner and crank snout. Can't do this on an externally balanced engine like a 400sbc or a 454. The fit should be close, 0.0005 to 0.001 so the balancer can't "waller" during acceleration/deceleration. We have an ancient key way machine that can actually do this with the engine assembled but by the time the front clip is pulled and the machine set up a Bridgeport would probably save money. Machine is now used by a friend to put new key way for drive pulleys/sprockets on ditching machines. When one of these machines is down price is not discussed to get it back in action. X2 on replacement.

Evan