What they said, plus, don't forget the lid area under the hatch, and the hatch itself. Check the firewall closely.
Don't be afraid to pull up carpet to check either. It's not hard to put in and take out. Better now than later, and if he doesn't like that idea, pass.
He says it's not running...just make sure it HASN'T been driven around with that blown head gasket and coolant in the oil. Otherwise that engine's not worth much.
Good luck!