Actor Robert Ridgely began his association with Filmation when he was cast as Steve Exhaustion, the $6.95 Man (a parody of ABC's Six Million Dollar Man) on Uncle Croc's Block. He comes off sounding more like he's doing a John Wayne impersonation than trying to approximate Lee Majors' voice, but, well, you can't have everything.
Charles Nelson Reilly (Uncle Croc) had done some voice work, starting with the syndicated holiday special, The City That Forgot About Christmas, but it would be 6 years before he landed another voice-over gig, taking over the part of Frank Frankenstone on The Flintstone Comedy Show. I cannot be certain, but I think Reilly was on leave from Match Game when he took the Uncle Croc gig.
To complete our trifecta, Jonathan Harris, who gets to invoke his Lost In Space catchphrase as Basil Bitterbottom, had made his voice-over debut in The Three Musketeers, part of the Banana Splits anthology series in 1968, and was the lone cast member to reprise when Hanna-Barbera adapted Lost into a Saturday Superstar Movie in 1973.
Back to Ridgely. He would enjoy greater success in his voice work, starting with Tarzan, Lord of the Jungle, and followed up with Flash Gordon & Thundarr the Barbarian, but did you know his career had started several years earlier? One of his earliest live-action jobs was in an episode of Kraft Suspense Theatre in 1964, which was later repackaged as the feature film, "Nightmare in Chicago", co-starring Ted Knight.
Muttley16 supplied this 2 1/2 minute snippet of silliness.