Your best external indicator of just how hot it got will be to look at the block where it meets the cylinder head right underneath the thermostat housing. The block is painted red and if it got hot enough to change the color of the paint or in the extreme instance, cooked it right off, then you should probably take a pass on it or at very least expect serious piston damage when you take the head off. It gets hottest in that corner of the block so make sure you heavily scrutinize that front piston and bore. Check for scoring or galding of the aluminum piston on to the steel bore. When they get hot enough it will actually melt the piston away and you can see the exposed rings. Not to bum you out but any car that does not run (unless it is something rare or special) is worth no more than fifty bucks, especially when you know that the cause is a blown motor.