For the sake of a complete answer, at the September 1, 1968 Can-Am, Sterling Moss drove the Pete Estes '68 Z/28 convertible (1 of 1 made) as the pace car and it had a cowl induction hood on it. It may not have been installed on the assembly line (there is no definitive proof either way) but it was installed on the car by GM, probably at the Tech Center. This is many months before any '69 got it.