What does "COPO" mean?
"Central Office Purchase Order"
I always thought the P was for production.
as always, could be wrong.
I think you are correct on (production).
Also I was under the impression that they rated the 69 ZL1 at 430HP same as the L88 and the it was the L71 that was rated at 435HP.
Understand that I was not very old in 69 and I could be wrong, Don