The "correct" height is not necessarily a specific number if the heads are not new, uncut units. I have valve depth numbers for new heads that I do regularly. Used or one-off stuff, I put it where I think it will work best. Often on used heads, it can be a challenge to get a good repeatable spot that doesn't "sink" the valve. Sometimes it is just a judgement call. Sometimes on a freshen up of street stuff the depth can vary by necessity, and touching up the tips gets the top height the same. Intakes and exhausts may come out different up top, but all intakes should be the same, all exhausts the same, for keeping the valvetrain and pushrods happy.
I use a set-up valve, and a dial indicator on a deck bridge, combined with an indicator on the quill of the machine. Find your depth, zero the machine to it, etc.
Leveling with a bubble in a guide hole can get you close, provided your machine is level. Indicating your fixture is the absolute way to know you are 90° to the quill, and "level". I have several spots that are doweled in my machine for some various common heads, to reduce set-up time. Take all that with a grain of salt, and do some ciphering of your own. Hope this helps you.....
