This is most likely an out of sequence episode. It was obviously held over from early in season 7 as it bears a 1969(MCMLXIX) copyright date instead of 1970(MCMLXX). It seems like it really belongs right before the two part "Kathy Jo's First Birthday" and "Goodbye Mr. Chimp", as the ending of this episode is a set up for that two-parter.
Nora Denney was credited as Dodo Denny, Nancy Marlow was credited as Nancy Marlowe, and Peggy Russell was credited as Peggy Russel. The latter may be a typo on the closing credits.
Ironically, and sadly, the same day this episode first aired, Byron Foulger, who had played Wendell Gibbs, the engineer of the Cannonball the previous season, passed away.
Though it's widely claimed that the PJ cast appeared on "Beverly Hillbillies" again the season after they were canceled, no such reunion occurred. The only PJ character to ever appear again after this episode aired? Was Sam Drucker, via his "Green Acres" association.
Though Mike Minor and Lori Saunders would appear a few times in 'Beverly Hillbillies' the following season, they'd play new characters. Similarly, the dog known as Higgins and Edgar Buchanan would reunite later in the decade to appear in the first "Benji" movie.
The final episode. The show wasn't canceled due to CBS' famed "rural cleansing" which led to an end of its fellow Paul Henning sitcoms "Beverly Hillbillies" and "Green Acres" (they'd both last a season longer), but just due to declining ratings. No proper finale was ever given, as none of the cast was truly aware this would be it for the show.