You want clear fire rings on the head gasket sealing areas with no carbon or rust on them. It would be a small spot on the circle of the fire ring. Check for signs of coolant on the top oiled side of the head. As the engine ran fine till the bottom end let go they are either fine or coolant in the oil ruined the bottom end. Possible a crack elsewhere in the block dumped coolant.
At that price snag them after a quick crack check and check them out closer later.
I ended up buying them. Felt pretty comfortable with them. The guys been a mechanic for 30 some years. Plus most of that times been with 6.2 and 6.5's.