318 build advise

Just mill the heads you have, they probably 68cc stock "675" heads? Mill .030 off for a 62cc chamber 'at the most'.
Dont bother spending on another head that flows worse without modifying it first when you have a good flowing '318 head' already that can be milled. To really make it worth while.. you would set it up for quench *with different pistons altogether.

Dont overthink the cam.