Just wondering if someone might tell me more about the heads I have. Did they come on a 340? The Allpar site has a listing that doesn't include what I have. I'm familiar with the X and J heads from various 340 cars I've had over many years but I've never seen O and Z heads on anything before. My engine has one of each. I first assumed someone just put a mismatched set on the engine prior to my purchasing it but they both have the same casting number 3418915 and each have casting dates within the same month of October, 1969. They do have 2.02 intake valves. I thought they might have been born on a 360 until I saw the casting date which is not correct according to Allpar.