With either of those cams, you'll definitely need to check your piston to valve clearance. I've heard that the F cam is the biggest of the FRPP cams you can run without piston modification, but you're still supposed to check clearance anyway. What made you decide on the X or Z cams? I'm sure there's better cams out there, especially with a split pattern design to help the often asthmatic exhaust ports on stock Ford heads. Also, with that much lift (.542 for the X or .552 for the Z), you'd definitely need to upgrade the springs on there, or you may have some pretty bad coil bind issues.