(written from a Production point of view)
Kellett filmed his scenes for "Mirror, Mirror" on Wednesday 2 August 1967 at Desilu Stage 10. He filmed his scenes for "Spock's Brain" on Wednesday 10 July 1968 at Paramount Stage 3, and his scenes for "Day of the Dove" on Wednesday 28 August 1968 and Thursday 29 August 1968 at Desilu Stage 9.
He performed stunts and made numerous appearances on the Western television series Gunsmoke. Other TV shows on which he appeared include Branded (in an episode with Michael Ansara), The Man from U.N.C.L.E. (with Robert DoQui), Mission: Impossible, Mannix (with Barbara Babcock and John Colicos), The Big Valley (working with Peter Brocco, Bill Catching, Vince Deadrick, Leslie Parrish, Bill Quinn, and Paul Sorenson), and Land of the Giants (with Don Marshall). He doubled for Gene Dynarski in two episodes of Batman, which also featured Grant Woods and stuntmen Hubie Kerns, Sr., Victor Paul, Dick Crockett, and Al Wyatt.
He also had small roles in films like Canadian Pacific (1949, starring Jane Wyatt), Bright Leaf (with Jeff Corey and Celia Lovsky), The Enforcer (1951), Angel Face (1952, starring Jean Simmons and Kenneth Tobey), and 5 Against the House (1955, with Brian Keith) and appeared as an extra in the Elvis Presley movies It Happened at the World's Fair (1963, co-starring Yvonne Craig, Gary Lockwood, Bill Quinn, and Guy Raymond) and Viva Las Vegas (1964, also featuring Terri Garr, Lance LeGault, William Meader, and Edwin Rochelle).