1982, when I was 20. I picked up a Hot Rod Magazine special edition on Camaros and these two articles were inside. The "ZL-1" article explained the "COPO" term and that the car was a special-order. The ZL-1 article also mentioned Fred Gibb Chevrolet and Yenko Chevrolet. The "427/425" article on the next page explained the availability of the L72 in the '69 Camaro.
