what are x heads and how can you figure out if you gottem?
They're good cylinder heads! I use J heads in my 318 which are supposed to very similar to X heads (many say the X are superior to the J's)
Have you already decided on pistons for your 318? The X heads may drop your compression ratio below standard if you use standard pistons.
My combustion chambers on my J heads with 2.02/1.6 valves were spot on 66.5cc which was the same as my standard 318 heads with 1.78/1.5 valves.
Though it looked like my J heads had some milling to get the chambers that small. there's no way to tell for sure how much milling was done before I bought them.
Hope this helps.