How Much Can Heads Improve Compression???

Machine the block to achieve a 'zero' deck and use a thinner head gasket. Unless you have about 9.5 or higher compression ratio leave those aftermarket cams in the box… they won't help.

You may want to find a pair of 302/308 heads from an 80's 318. Mill 'em down. They have smaller swirl combustion chambers.

I have a set of 360 J heads that have been angle milled and, with a flat top piston, we figure the compression will be around 12-1 which is just right for the engine we are building.