Hitchcock Fired Roy Thinnes as Adamson
Villain Arthur Adamson was originally played by TV actor Roy Thinnes ("The Invaders") who had just appeared as the villain in "The Hindenberg."
Hitchcock introduced Thinnes at a press conference as "Roy Scheider" (one of the actors Hitchcock had asked to play Adamson, along with Burt Reynolds), suggesting Hitchcock regretted hiring Thinnes.
Roy Thinnes filmed "Family Plot" for a few weeks before Hitchcock fired him and replaced him with William Devane. Thinnes confronted Hitchcock at a restaurant and asked why he was fired: "You were too nice for the role," Hitchcock said. (But Thinnes had clashed with Hitchcock too often.)
You can see a photo of Roy Thinnes as Adamson (with Dern, Black, and Harris) on the "photos" page of this imdb.com "Family Plot" site.
Thinnes is still in "Family Plot," from behind, carrying the bishop out of the cathedral.