Paul,
When things get hot enough to torch out valves like that, it can cause all kinds of collateral damage.
At the least, that head will probably need valve guides and the seats machined for the new centerline described by the replacement guides. The primary way a valve has to rid itself of heat is it's contact with the seat and the guide. When the margin is burned away like that, you just gots to know the guide has been seriously impacted as well.
If the guides somehow survived and you decide to see if it's a worth a roll of the dice, you can check to see if there is any seat face damage with lapping compound and a fresh set of valves. Clean the guides throughly with a bottle brush, oil the stems of the valves, and put a small amount of compound on the seat face of a fresh valve. Drop the valve down for a quick back and forth twist of less than 30* rotation, pick it up, rotate it 90*, drop it back down and twist it a few more times . Now check the contact pattern on the valve seat in the head If you don;t see contact all the way around, send that head out to the garden, it's done.
edit In order for that test to be valid, the guides must be in spec. A loose guide will allow the valve to wobble enough to give false results.
edit2and don;t spin the valve with a drill, do it by hand with only a small bit of rotation. Making full rotations will give false tells, you just want to do it enough to form a pattern.
It goes without saying it will need to have it's deck resurfaced. Hopefully your machinist has good ears, as there is a noticeable difference in the sound of "killed" areas passing under the cutter.
It's also worth noting the seats are a press fit into the head. When sh*t gets that hot they can lose some of their register, ... and nothing good comes from a seat coming loose. Only seen it a couple of times on a 4g, but the results were spectacular (snapped valve heads wedged in pistons)
If it survived, I would not use that head on a high end/comprehensive build.
... to be honest with you, I would just pitch that bitch ... you gots plenty more /ubbthreads/images/graemlins/grin.gif