In the final dance number there is a man in "Dr Frank N Furter" drag attire from "The Rocky Horror Picture Show" an homage to the next era of Musicals in the early 1970s.
Towards the end of the episode, Miss Codwell (Kristin Chenoweth) says "Add 'em up, kiddos, add 'em up."
This line is taken from Stephen Sondheim's musical Company, where it's also spoken to the main protagonist.