what are x heads and how can you figure out if you gottem?

The X means that those were second-hand with flaws from the factory but were good enough to run....you should ship them to me immediately where I can dispose of them properly!!

Actually many claim those were the best factory small block heads you could buy. Should be a 2.02" intake and 1.60 exhaust valve. Decent heads.
How did the 318 run? The chambers are larger on the x head so either someone put high compression pistons in the 318, possibly decked the block/milled the heads, milled the heads, or just threw em on.
Definitely have them cc'd before you reuse em.