Now correct me if Im wrong, but didn Andy appear in Gomer Pyle, USMC?
Yes, twice in fact. One episode concerned Opie’s running away to join the Marines; the other was when Gomer came back to Mayberry on leave, only to find that the Taylor family and Goober were away on a camping trip. Many, many familiar faces from Mayberry were seen in episodes of Gomer Pyle – USMC (too many to list here; there must be at least 100 of them), but the only actors to play the same characters on both shows were Gomer, Goober, Andy, Aunt Bee, Opie, and Sgt. Carter.
