All of the above, from both Drew and Craig, but especially this:
Originally Posted by g96nt
Any time the head comes off, you should be dropping it off at a machine shop to be planed. I always have my guy inspect it, and adjust guides/replace valve seals.
If you're looking to have minimal downtime, buy a junkyard head and have it re-worked prior to dismantling. do NOT put a gasket under a non-planed head.
The HG kit comes with valve seals for a reason, so order that first and send them off with the head to the machine shop. Depending on the shop and the work done, you can expect to pay anywhere from $250-$350 to have the head cleaned, planed, valve seals replaced, and valves lapped in. You shouldn't need a full regrind of valves and seats...