The 3 tones heard when Moe slaps Larry and Shemp for not reminding him to get the salad and the cake was the 3-tone identifier for NBC known as the NBC Chimes that date back to at least the early 1930s (obviously originating on radio).
The first two initials of Emile Sitka's character, B. K. Doaks, may be a reference to Buster Keaton, who was writer Clyde Bruckman's friend and sometimes collaborator.
The newspaper shown at the beginning contains excerpts from the Dec 14, 1938 issue of The New York Times.
Production number 4107.