The Slingerland copper-over-wood finish is very rare and extremely hard to find. To make matters worse, it was a finish that pitted badly over time. I had a pristine original 13/16/22 that I had bought brand new in 73. That color was only in the line for a very short time. Anyhow, like a dummy I sold them a few years later and always regretted it. Any copper Slingerland drums that I have seen in the recent past have all had bad pitting. The only decent set I saw was one owned by a friend of mine Robert Bowler, out at A Drummer's Tradition in San Rafael, CA. This goes back about 5-6 years, and the kit was really rare: 12/14/20 with 6" and 8" matching bongos and a matching SD, and, there was very little pitting. The kit was $2500 and I balked. I called him back a week later and it was gone. Should have grabbed it. That kit would cost a lot more today. My advice, if you find a clean copper over wood kit from the 70s grab it!
Keep on Pl Steve