I wouldn't try an easyout, headbolts are TIGHT and I've broken them at far lower torques - you'll never get the fucker out if it shears off!

I'd try and tighten it first, as said. I also like Jon@work's idea of drilling slightly then retrying the socket.

Might be easier to get square onto the bolt to drill it with the engine out, less risk of damaging the head then

See if you can get some tape round the area inside the head to minimise swarf, I cleaned mine in a parts washer then flushed it out thoroughly with a hosepipe as I was paranoid about swarf from the skim