Chris, my assumption that the lines were copper plated was based on that they were brazed into the cups. After reading your comment though, I realized that I did not really know if you can braze to copper or not (still don't). So I took a closer look.
I was able to sand off a section of the copper plating, and I even used some gun bluing on it. Sure enough the sanded section took the color OK. Of course that's not to say that they did not use copper lines on some of their covers, only that these recently purchased ones have steel.