For all of his accomplishments in animation, Frank Welker has never had a regular live-action gig. The closest he came was an unsold pilot for ABC in 1973.
Frank is part of the ensemble, headed by Richard Dreyfuss, in an adaptation of Joseph Heller's Catch-22, which Paramount was hoping would be a challenger to a well known CBS series, M*A*S*H, which, like Catch-22, had first been in theatres three years earlier, but was far more successful.
Frank first appears around the 3:50 mark as a pilot, and, danged if he doesn't sound like he's using his Fred Jones voice from Scooby-Doo.
More on Catch-22 over at The Land of Whatever.