Vavle stem height....

Sorry, but if I picked up a set of (shaft mounted rocker) heads from a machine shop and the valve tips were not level, that would be the last set of my heads they would ever do. Hydraulic lifter preload can only compensate for so much.

Since you are planning to run adjustable rockers, you can set the preload anywhere you want. A reasonable work-around. You could also have the valve tips ground to level them out, run lash caps, etc...

If you feel you must level the tips, and performance is your main goal with this engine, consider oversize intake valves. This way the machinist can set them higher on their seats (good) as opposed to lowering the exhaust valves into their seats to raise the tips (not as good). This will provide the side benefits of a slightly reduced chamber volume, and some flow improvements (so long as you open up the bowl).