Hey there @I_love_Cat_Stevens, there’s quite a lot of casting differences that would surprise you
Charles Bronson and James Coburn were both offered Clint Eastwood’s Man with No Name; Bronson said the story made no sense to him and he turned it down. James Coburn was interested, but he balked at the $15,000 paycheck, and his own asking fee was too high, so he turned it down.
Since Leone tended to fabricate and stretch the truth quite often, a slew of names were reported to have been offered the part, including Eastwood’s Rawhide costar Eric Fleming. Richard Harrison has said in numerous interviews he was indeed offered the part and had also indeed recommended Clint.
Frank Wolff was the original choice for Ramon Rojo in a Fistful of Dollars and was interested, but he bowed out when he and Leone clashed over each other’s interpretation of the character. Giorgio "George " Ardisson was also offered the role of Ramon, but either he was too busy, or felt the part was beneath him at the time. That he said he regretted that decision not long before his passing could confirm either.
Clint Eastwood and James Coburn were both in consideration for the role of Harmonica in Once Upon a Time in the West, but Eastwood didn’t have time as he had other projects going, and I’m guessing Coburn thought the price tag too low again. Ironically, Eastwood wanted Leone to direct Hang 'Em High, but Leone was busy with Once Upon a Time in the West.
Charles Bronson was offered the role of Angel Eyes in The Good, the Bad, and the Ugly, but again the script didn’t make any sense to him and he turned it down. Gian Maria Volonte was an early candidate for the role of Tuco, but he and Leone clashed so much on the previous films he automatically turned it down.
Eli Wallach was originally set to play Juan Miranda in Duck You Sucker, but the other producers insisted on Rod Steiger. Leone had to veto Wallach’s contract, and the two stopped speaking to each other. In pre production of the film, Jason Robards and Malcolm McDowell were in the running for the John Mallory character before James Coburn finally thought the price tag right to work with Leone.