I use stock replacement forged pistons. I got the drop in compression from the chamber work on the cylinder heads. The #62 heads already had bigger chambers than the 421 heads. The engine had just under 9.6 to 1 compression. Years later I used those very same heads on my wife's 1962 389 to temporarily be able to run the car on 89 octane while I built a new engine. The engine would not run even on 93 octane with the 389's original heads.
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