Complex sentence: Boyd had in mind two young, then unknown actors, David Soul and Sam Elliott he had seen them in a beer commercial that was based on Butch Cassidy and the Sundance Kid and thought they had the chemistry of Newman and Redford.
Split into simpler sentences: Boyd had in mind two young, then unknown actors, David Soul and Sam Elliott. He had seen them in a beer commercial that was based on Butch Cassidy and the Sundance Kid and thought they had the chemistry of Newman and Redford.