The final acting credit in the end titles is '...and Carlton Duffy as Himself'. "Carlton Duffy" is a thinly-disguised Raymond Burr playing an uncredited dual role opposite himself, courtesy of visual effects by Albert Whitlock.
William Katt, who plays "Jimmy", is the son of Raymond Burr's former Perry Mason (1957) co-star Barbara Hale. Years later Katt and Burr would work together again, along with Hale, in the "Perry Mason" movies, with Katt playing the role of "Paul Drake Jr.".
Raymond Burr, Ironside, also played a dual role in Perry Mason, as a merchant seamen.