The telephone number on the phone in the phone booth is (311) 555-2368. This was a unique 10 digit phone number (including the nonexistent area code of 311) was set aside by AT&T as a "safe number" for use in movies and TV shows starting in the early 1960's. This 10 digit number is seen in a number of shows and movies until the 1980's; it's even the home phone number of Jim Rockford, as seen every week during the opening credits of The Rockford Files.
The receipt from the trailer park is dated 8-20-69. It's a common practice to date items during production with the date of filming, indicating that this episode was filmed in the end of August 1969, which would coincide with its subsequent air date of 11-22-1969.
This episode includes several rare appearances of Peggy Fair's blue Simca 1000. Only the 3rd episode, to date, to include her car. Conversely, Mannix's dark green, customized Dodge Dart convertible does not appear.
The phone booth Peggy is in is by Herbert's Delicatessen. That's the movie set where Robert Conrad sat in "The Playground."
Fourth and last appearance of Frank Campanella, older brother of Joseph Campanella who played Mannix's boss in the first season of the series.