I know the recall was in place in 1972, for the 1969 Z-28's. It would be hard to believe that the mounts would be rotted away by that time. I would think it would be a problem with too many hard leaves breaking the mount. GM was known to change the mounts to interlocking style, if tubing headers had been installed, and the kit would not fit around the exhuast.
My '69 RS L65 received the pictured (JohnZ) recall cable motor mount strap in '72. It was not just for the Z28s. Installed in a very short time as I recall. I also agree the mount would not be rotted away after such a short time. Lots of "hard leaves" around at that time with so many Camaros, Mustangs, and assorted other muscle on the street!