This came in a large through the mail collection I recently purchased. The collector was meticulous and kept the return envelopes. This one was returned in 1987. He had included an additional Dodger post card of Koufax that was returned unsigned.
I figured if he was using a ghost signer they would have signed both. It just looked too close to his autograph for me to believe it was secretarial. It obviously is not a recent forgery attempt but you could be right and it might be secretarial.