I rebuilt a set of them . 1971-72 350 Heads 74cc chambers . I installed all new S/S valves and Z/28 Springs with Performance Retainers and Locks . With .015" shim Head Gaskets and Flat Top Pistons you should be right about 9.1 C/R . 300 H.P not a Problem I would say by the way the Ports Looked they are about the Best 74-76cc Smog Heads and not a thin casting . With a Good Dual Plane intake 450"-460" Lift 216-218 at .050 dur 110 L/C Camshaft and a Set of Headers it will be near 350 H.P and run on Low octane Fuel every day trouble free .