Walt Disney's 1976 sports comedy, "Gus", offers a trifecta of familiar voices in this sample clip, two of whom would begin work in animation after the release of this film.
Bing, bang, boom! Start with Edward Asner (on a break from The Mary Tyler Moore Show), who would resurrect his career by moving to voice acting in the 90's (i.e. Spider-Man, Batman: The Animated Series). You can see Louise "Liberty" Williams behind him, and alongside Louise, we have Ronnie Schell (ex-Goober & The Ghost Chasers, Gomer Pyle, USMC, Good Morning World), who would return to toons 2 years later with Battle of the Planets. Not seen in the video are Happy Days' Tom Bosley, who would turn to voice work toward the end of his Days run (The World of David The Gnome), after having worked on Wait 'Til Your Father Gets Home right before Days, & Harvey Korman (Great Gazoo from The Flintstones). The all-star cast also includes Don Knotts, Bob Crane, former NFLers Dick Butkus & Johnny Unitas, the latter playing himself as a sportscaster, and Tim Conway. Hasn't been seen on TV in years.