I would follow Jim's advice as he has a lot of experience in the area.....BUT FWIW, I figured I'd throw this out there. Those are the heads my friend has on his car nicknamed "5300". It's a 76 Grand Fury wagon that weighs 5300 pounds and runs 12.80s with a stock bore and stroke 440. They are unported. I was not aware they were more prone to cracking. But then I have not seen that many, either. They can be made to work obviously, if that's what you have.