The first person seen - the young blond-haired man getting off the elevator, delivering newspapers - appeared, regularly, as an 'extra' in the background, as one of the WJM staff members (who in one episode of that series, said his name was 'Peter'), on the The Mary Tyler Moore Show (1970) show, during it's first few years, is an actor named J. Benjamin Chulay (the 'J' is for 'John').
Even though this episode is from the series' 4th year, the opening credits used are those used during years 1-3, and not the one which had been, since the 4th year began.
The glass - on a rope, which Mr. Carlin has on, at the Drs. Walburn/Hartley office-warming party (named a 'swinger' glass), was a novelty (gag) gift, sold at the time (www.alleewillis.com/museumofkitsch/pages/drink/swinger-party-glass.html).
The scene titles and accompanying ragtime music, are an homage to the same elements in the movie "The Sting", which was released 2 years earlier.
This episode has the first mention of Howard's brother, Gordon Borden (who's a - you guess it; game warden), or as he's known; 'warden Gordon Borden'. An entire episode devoted to both him, and things which rhyme, appears later in this season (episode 18, of the 4th series). This, time, however, warden Gordon Borden isn't seen. He's mentioned as stopping by on his way to...Jordan.