yes when you MILL the head, it brings down the head close to the block. What it does is move the cam positioning as well. You can bring it back the cam adjustment with a Cam gear. So keep in mind when tuning, that when at ZERO, you are actually not at ZERO and you have to compensate for that during the adjustments.
Milling is not the best way to gain performance, but if you are going to do it anyway, dont do more than 30 thou. off the head. Just to keep it safe and if you plan on doing any bottom end work later on, you havent taken too much off the head to have any valve clearance issues on high compression pistons.
Wil