1970 Dodge Dart with a 440 burned the head gasket, what caused this?

That happened to the numbers matching 440 in my 69 Coronet R/T, The previous owner let his younger brother rebuild it in High School Shop class. They had it bored, but I'm guessing they didn't mill the heads and didn't deck the block. The car originally had a 2 core 22" radiator that frequently overheated I found out after I bought it. It might not have helped when I put a solid lifter .310 duration Crower cam in it. It sounded nice for about a hundred miles.:rofl: