my speed-pro catalog states; 9.77:1 with 78.5cc chambers and 8.94:1 with 88cc chambers. this assumes a .039 gasket. a .020" steel shim will have the quench distance too tight, a .039" gasket will get quench distance around .045"; assuming block hasn't been cut. if it were me i'd leave the heads at 80+ cc's with a fel-pro 8519 gasket to run pump gas. i did something similar to what you have but used 84cc 906 heads and seems to have worked fine with pump gas.