The fictional movie that Redd Foxx is promoting is titled "Windows are a Pane in the Glass", a joking reference to Foxx's real life demand that his dressing room have windows. (The studio's refusal led Foxx to leave the series for portions of the third and fourth seasons.)
When Fred reads the newspaper ad about the Redd Foxx Look-Alike Contest, he says Redd Foxx will appear at NBC at Studio 3, which was the same studio where Sanford and Son (1972) was filmed.