One of the advantages of the KB piston is that it has a stable expansion rate, it does not expand very much when it gets hot. This allows a smaller running clearance, less piston rocking in the bores, and better ring seal. But the silicone in the alloy does make them brittle, they do not like detonation, and I think they would not like to be slapping around in a bore as well. I know that if they are run loose you will sacrifice some ring seal. I know it is tempting to save a few bucks, but just do it right, if the block is good enough to use, buy pistons to fit, if the block is questionable get a different one and bore it to fit the pistons. You will be much happier in the long term.