I wonder if GM changed/ improved the later or replacement castings. They had to know that there was a problem based on warranty claims and replacement head sales. I do remember that my 79 was very lean mixture possibly helping to crack heads. When I put on the new head I also adapted an autolite 2bbl from a 400 Ford station wagon that was richer than stock but not too rich. (Light brown plugs ect.) Do you remember if any replacement heads cracked also? Jay
