Richard Donner, the episode's director, has a cameo as the guy talking to the lady at the bar when Don Rickles has a drink. The lady is Mindy Rickles, Don's daughter.
The name of The Ventriloquist, "Mr. Ingels," is a reference to legendary horror artist Graham Ingels. Ingels is best known for his work of "The Old Witch" from The Haunt of Fear, the sister title of Tales From the Crypt published by E.C. After horror comics were vilified and ceased to be published in the mid 1950s, Ingels relocated to Florida and became a recluse. Although he taught art lessons and was well regarded in his community, friends and former associates were clueless as to his whereabouts, or even if he were still alive.
The name of the ventriloquist act (seen on the autographed picture given to Young Billy Goldman in the opening) is "Morty & Ingels." It seems obvious that this is an "inside" tip of the hat to the comedian Marty Ingels (1936-2015).
Billy Goldman's character is most likely named after famous screenwriter William Goldman