Lawford played Pepper.....that's the level of humor
At least Sammy would still work with him. I'm sure the makers of Salt & Pepper hoped to capture some of the spirit of the Rat Pack by casting Lawford and Davis, thereby giving the film the appearance of being another in the series of films started with Oceans 11 (1960) and ended with Robin and the 7 Hoods (1964). Unfortunately, it was not up to the caliber of even something like 4 for Texas (1963), nor was the Rat Pack's style aligned with the zeitgeist of the time.
And because it was 1968, Salt & Pepper's creators not only tried to appeal to Sinatra's audience, they targeted younger audiences by setting the film in swinging London and embracing the aesthetic of the drug culture. It's cocktail culture meet counterculture. It's sort of like the Monkees and the Jimi Hendrix Experience touring together or William Shatner doing "Lucy in the Sky with Diamonds" or Nixon appearing on "Laugh-In." And to think it all actually happened...
Incidentally, it was directed by Richard Donner, who also did Superman: The Movie (1978) and the Lethal Weapon movies. After Salt & Pepper, he spent a couple of years directing episodes of "The Banana Splits Adventure Hour."
Based on this trailer, it looks as if they used a scene straight out of the Beatles' Help!. Can you spot it?:
What's truly amazing is that a sequel actually got made two years later called One More Time (its tagline was "Never before were they together again for the second time!"). And just to stoke the coals of the Sinatra/Rat Pack-Lawford grudge, Dean Martin's ex-partner Jerry Lewis directed it.