what can i expect 318 with x heads

it's .0048 for every cc, they might be around 72cc now- -8cc [.038] then figure in a .039-.041 aftermarket head gasket and the push rod worry pretty much go's away.
Stock gasket is around .019 thick, so you changed/increased it around .020 pre load.

in that instance he would have the 68cc that those 318 heads are, so no cyl psi loss
though it would not make the 65cc mark and help the low end/response...unless he stayed with the thin shim or mill another 4cc off for a total of 12cc to make up for that .039 gasket and really get 65cc psi
who knows what the pre load is now with worn parts then on the other side..worn seats sunken valves...

good idea rob.
better check it out.