it could be head gasket or cracked head, no real way of knowing until the head comes off. But your right, these engines aren't very forgiving when it comes to overheating them. after changing my timing belt/water pump etc... a few years ago I did pretty much the same thing. after the job was done and I bled what I thought was all the air out of the coolant, I took off with the tunes pumping and 5 minutes later looked at my gauge and was touching the red. I got lucky though!

sorry about your luck!