I think I read somewhere that the financial 'backers' behind the Film had 'insisted' that Leone hire a 'big name' like Rod Steiger - in order to 'sell' the film....? I could be wrong?
Rod Steiger had previously received glowing accolades for his performance in 'In The Heat of the Night' (another magnificent Film, directed by Norman Jewison), as a bigoted Lawman, playing next to the great Sidney Pottier.
Even though Leone had already promised the role of 'Juan' to the ever-superb Eli Wallach - Leone had to 'bend' to the Financial backers demands, and hire Steiger, instead.
Leone and Wallach, who had had a very amiable relationship up until this time (The Good, The Bad, and the Ugly), did, I understand, fall out for many years over this issue, but eventually 'made up'.
Someone please correct me if I'm wrong about any of this.....