Bill Mumy (Googie) was the original choice for Eddie Munster, but his parents didn't approve of the extensive makeup that would be used for his character.
The "pin-up" pictures in Grandpa's old trunk are actually various characters from some classic horror films. Among them is Lon Chaney as the Phantom of the Opera, Lon Chaney as the vampire in London After Midnight, Mr. Hyde from Abbott and Costello meet Dr. Jekyll and Mr. Hyde, Boris Karloff from the 1935 version of The Raven, Bela Lugosi as Dracula, Lon Chaney Jr as the Wolf Man, the Gill-Man from Creature From the Black Lagoon, the werewolf from Hammer's Curse of the Werewolf, and one of the Mole People, among other creatures
Butch Patrick and Billy Mumy both played in "A Child is Waiting" (1963).