Dude, it's the X. You should see the Chevy guys fighting over the old 041X double humps. You'd think they were made outta gold. ......and every single Ford 400......has a row of X's cast right in the intake valley. You caint tell um nuthin, until you show um another one just like it and they they think they have seen two "rare and experimental" blocks. Yes, the X marks the spot. The stupid spot.