Well, yes. 12 mm engines are JK, CY, ME, MF, and, I still swear CR's were all 12 mm...although I had one guy say otherwise. I never saw proof of his claim...and he was a "new" guy.
CK may have started out as 11 then 12. The CR, JK, and CY's sure seem to have a slight amount more nickel in the cast as they hold a (lack-of) ridge much better than the seemingly butter-soft ME's. I think those even CAME pre-ridged! (juss kiddin').