6X-4 heads typically come in around 92cc in the combustion chambers. If you deck/square the block for close to zero, .039" Felpro head gasket and take a little off the heads you'll be closer to 10 to 1 than 9.5 to 1.
The camshaft is a huge player in being ablt to manage pump gas at any given compression ratio. I ran a 455 with 6X-4 heads on it and it was fine with lower 87-89 octane fuel. I typically kept 92-93 in it but it alctial
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73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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