Complex sentence: Producers Mark Goodson and Bill Todman hired him for their game show "Two for the Money"; when the show's usual host, Herb Shriner, had other commitments during the summer of 1954, O'Keefe took over for three months.
Split into simpler sentences: Producers Mark Goodson and Bill Todman hired him for their game show "Two for the Money". When the show's usual host, Herb Shriner, had other commitments during the summer of 1954, O'Keefe took over for three months.