From the sounds of it I don't know if it's head gasket for certain. He says there's lots of smoke and stuff, but doesn't necessarily mean head gasket. Personally I would check oil and see if it has coolant in it (milkshake). I would check the coolant for signs of oil, and coolant level because if the coolant is low and it's not leaking outside the engine it may be going into it and being burned. The color of spark plugs can determine what was burned by the plug so a picture of each plug would help determine what cylinders did what. Do a pressure test on the cooling system, do a compression test on the motor (after checking that no cylinders have fluid sitting in them), and if things are checking out and the vehicle can be run (with all fluid checked and full) then you can do a coolant sniffer test that checks for exhaust gasses in the coolant. Just because an engine overheated and lost power doesn't mean head gasket. Could be a more severe failure. Personally I'm dealing with a head gasket issue on a Cherokee I just got and I plan to throw a whole engine in it because it's cheaper than buying a gasket kit and having the head machined.