The episode is a homage to The Untouchables (1959), not only in its title but in its plot center (a group of sharply-dressed characters going up against gangsters).
Big Gus is, ironically, a diminutive gangster. His design would be used for the Ant Hill Mob in Hanna-Barbera's later series Wacky Races (1968).
Jean Vander pyl who did the voice for fi fi was also the voice for Wilma Flintstone and they had similar appearance