In his (fantastic) biography on Sergio Leone, Something To Do With Death (p299), Christopher Frayling writes about Once Upon a Time in the West:
Stanley Kubrick admired the film as well. So much so, according to Leone, that he selected the music for Barry Lyndon before shooting the film in order to attempt a similar fusion of music and image. While he was preparing the film, he phoned Leone, who later recalled: 'Stanley Kubrick said to me, "I've got all Ennio Morricone's albums. Can you explain to me why I only seem to like the music he composed for your films?" To which I replied, "Don't worry. I didn't think much of Richard Strauss until I saw 2001!" Barry Lyndon could have been Once Upon a Time in Georgian England: the music, the choreography, the deliberate pace, the ritualized duels. Leone reckoned, though, that maybe Kubrick didn't quite have the common storyteller's touch to pull it off.