340 stroker 422

If you machined the pistons, the change in weight would likely do nothing to negatively effect the balance.

Read up on overbalance/underbalance and most engines run just fine in a range of 48-52% of bobweight. 50% being the typical bullseye. Say you had a 1900 bobweight, an acceptable range on that is 1862 to 1938

You are taking about 16 grams out of the bobweight with a 12 cc relief in the top on your piston.