Cowl Induction hoods in reality were kind of rare back in the day. The 1969 only ZL2 Cowl induction hood was an option on Z/28 AND SS models. Of the 243,085 '69 Camaros built only 10,026 Z/28's and SS's had that hood from the factory. There were 20,302 Z/28's and 33,932 '69 SS's built, so not even half of the Z/28's came out of the factory with the cowl hood.

EDIT: So that's a total of 54,234 Z/28's and SS's and 10,026 hoods, if split 50/50 between the two that's a little under one-in-five with the factory installed CI hood.
OOOh and I just remembered, of the 10,026 '69's that got the ZL2 hood, 3,675 were Z-11 SS Indy Pace Cars, that's over a third of them. Only leaves 6,351 for the rest of Z/28 and SS Camaro's.