The short clip of Gail Fisher (as Mannix' secretary, Peggy) used in the opening credits is taken from a scene near the end of this episode, when she walks into Mannix' office to announce that she's found the address for Harvey Templeton (Lee Bergere).
When Mannix enters the Artists and Model Club there is a full size cardboard figure of a model in a green bikini. This is the same prop that was used in "To Kill a Writer" (season 1 episode 23) in Montoya's secret shrine. Presumably in that episode the model was the girl in the unsolved murder case. In this episode when the second model comes up to pose, her outfit and look is similar to the cardboard one.
Billie told Mannix that most guys think of "love" as the tenth word in a telegram. She was referring to Western Union's policy at the time to charge a set price for the first ten words of a telegram (excluding the sender's name), then an additional amount for each word beyond ten. So a ten-word (i.e., minimum price) telegram from a man to a woman would end with "love" and the man's name.
The Richard Avedon psychedelic portraits of Ringo Starr and John Lennon adorn the walls of the Artists and Models Club studio. Paul McCartney's portrait is in the changing room. We must assume George Harrison is on the "fourth wall."
The radio in Harvey Templeton's office is a Hallicrafters SR-2000 "Hurricane" amateur radio transceiver with P-2000 power supply beside it. The radio was produced from 1965 to 1972.