Actually, all light and heavy cruisers used 8 inch shells. There were more than a few that were in service into the 70's. There were some that operated off of the coast of Vietnam, and my best friend's father (when I lived in Yokosuka, Japan as a kid) was the commanding officer of one of the heavy cruisers (Possibly the Oklahoma City...)
It is possible that these shells may have been stolen from various naval installations around the world. When I was a kid, they had acres of these surrounded with chain link fence, which we climbed over occassionally.
Bzzt. CLs had 6-inch guns.