Sorry to bring "bad news", however, The commonly available, (for the last 10 yrs),"stock" compression, "rebuilder" style Pistons for the 318, with 360 heads and a composition head gasket, will yield closer to around 8.0;1 for compression ?
The problem here is that the 1970 comp. distance Piston for the 318(which was higher than later 318's), has not been available for over a decade. Unless they used a Keith Black piston, you most probably have very low compression.
Use a small camshaft. 340 replacement 'musclecar" cam from Comp. Cams maybe ?