In the book Chevelle and El Camino ID Model Codes, published by the National Chevelle Owners Association, suggests 323 COPO Chevelles built based on the number of SS optioned bodies and number of engines built. See attachment.
As for insurance, can't remember how much the insurance was when I bought my COPO Chevelle in 1972 but I did find a certificate indicating a 10% surcharge on it.
Andy
The attachment didn't work. Here is a link to the page
Chevelle numbers