Hey, It's That Guy!: "Dog" was played by Higgins, who later went on to big-screen fame as "Benji".
The Hooterville Cannonball, Sierra Railroad No. 3, is no stranger to the screen, either, having appeared in countless westerns, films with Clint Eastwood, and even Back to the Future Part III, hence her nickname "the Movie Star Locomotive".
The Other Darrin: Of the three main girls; Betty Jo (played by Linda Kaye) was the only character whose actress remained the same throughout the show's run.