Ok I bought an absolutly mess of a 340 engine!!! I'm getting ready to take it back out of my car and I'm going to compleatly rip it down this time. The question that I have is this. The guy I bought it from claimed that it had X heads on it. What if any was the big advantage of the heads? How do you tell for sure that they are the X heads? And what kind of flow numbers should I expect from them if they are unported or basicly stock?