Thats kinda ironic. I also pulled apart a 69 340 w one X and one Z head. The production date on the heads were only 6 days apart so I was unsure if someone had been there or if it was towards the end of the X heads and they just assembled it that way. My uncle has a 70 340 duster he bought new and it now only has 14K mi. on it. It has one O and one U head and that thing has never been apart for a fact. He drove it 2 yrs and its been on blocks, on carpet, covered up in a heated garage ever since. Paint and interior still like new. Ive been trying to buy it for years. Still has original tires. Off white car, w/ black stripe and blue interior. Auto on column w bench, w wheel covers. Kinda plain looking but that is how it came.