They reference building the new building for "The Brooklyn Historical Society". At that time it was called "The Long Island Historical Society".
Morris says to Russell: "There's no need to talk as if I were your chauffeur." The word chauffeur was not in use then. It means stoker in French and was used to mean the driver of a steam-powered automobile who had to stoke the fire before the vehicle could be operated.
At the dinner table near the beginning, Bertha Russell is using a salt shaker. Salt (and pepper) shakers were not common until the 1920s. The ones in use in this scene date to the 1950s.