Scott, the date of the photo is correct and taken from the issue of Competition Press & Autoweek that it was found in. The first appearance of the cowl induction hood was on the 1 of 1 '68 Z/28 convertible owned by Chevrolet's Pete Estes. That hood was probably put on the car by the GM Tech Center and not as a production line component but it was present on the car when it paced the '68 Can-Am race at Road America. The second application of the cowl hood that I have seen is on the car shown in the Berger ad. This was a car used by Chevrolet for its new car introductions for '69 and it appeared in a large number of road tests in the fall of '68 as well as some print ads. You are correct that the first use of the cowl induction hood as a production line component was at the end of December '68 when they made their debut on the ZL-1 Camaros.
There is a highly documented hugger orange LA Z28 built 2nd or 3rd week dec with ZL2 and paper out the rear... it is now the earliest known ZL2 accompanied by supporting docs.