Though it's quite apparent that party hosts Johnny St. Clair and Jeff Levane are a gay couple, what's very unusual for this time is how 'normal', as in typical, they are. At this time, gays on television were usually played for laughs, i.e., the character John Ritter played on Three's Company (1976), was a straight man 'pretending' - in a very effeminate, over-the-top way.
Mr. Benz is identified by Rockford as a Mercedes Benz 220S convertible. The 220S was manufactured from 1956 to 1959. There were just over 3,400 220S convertibles produced.
When the conspirators are waiting behind the club, the building across the street has a sign 'No bicycles here' and there are several parked under the sign.
Rockford uses St Claire's name but also calls him by its traditional usage: Sinclair. Both are used.