The TRW piston says 10.0:1 because it's supposed to be a copy of the OEM piston. In reality, it's only 9.0:1. I'm not certain, but I think you'd be close to 10.0:1 with an 11.0:1 piston without decking or milling. I could be wrong, but if you don't want to deck or mill this may work.
