The bottom of the broadcast sheets on the #1 and # 2 ZL-1's contain the following information.
Ship 12/30 Estes requests red hot
Pilot 427 engine option 9560 BA
As Bill Porterfield was restoring the Gibb/Harrell race car, he made an alarming discovery. In this attempt to correctly restore the car using photos supplied by Fred Gibb, one part which presented somewhat of a mystery was the water pump. The one in the old photographs appeared to be a regular long-style passenger car pump, but it looked as if it were made of aluminum. The old parts book show an aluminum pump was used only on L-88/ZL-1 Corvettes. But that was a short-style pump. The books show that all big-block Camaros were equipped with the regular production cast iron pump! Bill found a collector friend who had a long-style aluminum pump that had been removed from an "engineering car" that had been purchased by a GM Tech Center employee. The body of the pump had a 3868811 casting number and was identical in appearance and shape to the cast-iron long-style pump.
A deal was made for the pump, and Bill went on to attempt to confirm the history of that number. He managed to make contact with a fellow who was a program manager during the development of the Mark I, II, III, and IV big block engines. He remembered an aluminum pump being released to production for the ZL-1, then cancelled a short time later when a problem was discovered. The bearing was loosening up and moving in the body of the pump during the durability test program. Since an original photograph of the #3 Berger ZL-1's engine shows a cast iron, Porterfield concluded that only the first two ZL1 Camaros were built with the aluminum pump. Porterfield was very satisfied that he was able to obtain a pump that "looked lik the one in the Gibb photo."
After all, the car was then one step closer to a 1969.
source: The 1969 Camaro Reference Book
by John R. Hooper