IF you use -8 cc for valve reliefs and .041 for a gasket thickness your compression comes out at about 8.75:1, which sounds about right. Most Pontiac stock pistons have 4 valve reliefs with a volume of 6 - 8 cc.
FWIW, Stewart
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1976 TA, nose converted to 1970 style, 406, ported #13 Heads, '70 iron intake without crossovers, Q-Jet - Cliff style, RARE OS manifolds, Pypes duals w/crossflow, UD 230/238 custom HR 4/7 swap cam with solid roller lifters  , Hydro-Boost 4-wheel discs, 4 Speed, 3.23 posi.
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