You will need to file gap the rings to get the proper top ring gap on the KB107 pistons. If you don't go by their specs expect to have trouble.
I for one have never balance my engine running them and it has never let me down. I know sever people running with KB pistons in both big and small blocks that haven't and have no problems or excessive vibrations and the engines have been very good longevity. None of us over twisting the engines and stick pretty close to 6000.