i have heard a few different things regarding this and felt i would run it by an expert.

is it the x11, x33, .. that makes it a z28?

x-33 or x-77 makes it a 69 z28. 68's didnt use x codes

x-33 or x-77 makes it a z28
......or no X at all.

i shouldve added that an early built norwood car, pre- x code could have been a z or a van nuys built car could also have been a z. these cars you have to look for "clues" or be lucky enough to have original drivetrain or documentation.

also, you might want to do some research at www.camaros.org its a really informative site on the 1st gen camaro.