I'm told the earliest known cowl hood used in production is roughly the last week of Dec 68 for the Norwood assembly plant.
I haven't heard anything about Van Nuys. Was there a timeline there as well??
There is a 12C Van Nuys Z/28 claimed to be the first ZL2 car but it is not possible to know that. The car was final assembled on or about December 26, 1968. At Norwood the earliest known ZL2 car is ZL1 #1 final assembled on or about December 30, 1968.
There may have been earlier cars but not by much. The system has numerous parts and they all had to be present. Broadcast copies exist for both cars and neither is noted "Pilot ZL2 build" as one might expect.
Excellent info, thanks for the reply William.