The open chamber heads came in a number of different chamber sizes, do you know casting numbers? Don't believe they used open chambers on the SS engines in 70 but they did have open chamber heads in 70. The open chambers will reduce the compression which can be good on a street car with the pump gases available today. You would need to know what pistons and other work was done to figure compression.
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Hank
70 Chevelle SS396(454), M20, 3.73
My Chevelle
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