It might screw into your Copal 3, but it doesn't screw into mine. I took the elements out of my (virtually unused) 360mm Tele-Xenar, and the Ektanon elements were not a match. Perhaps there was a machined step down ring already in place within the Copal shutter, and if that were removed it might screw in, but I would bet that some more $$$$ will flow into S.K. Grimes before any Ektanons are sitting in any Copals.
I certainly don't need two of the same lens, and once I get mine squared away, I'll let you know via PM.