Was this originally planned for Eastwood, Van Cleef and Wallach?

I know the story about how Leone wanted them to play the killers at the station in the beginning, but the three characters could easily have filled the roles of Harmonica, Frank and Cheyenne. Was this originally intended to be a 4th "Dollars" film?

Bronson's Harmonica is a little more unearthly and solemn than Eastwood's Man With No Name, and motivated by vengeance rather than financial gain. Fonda's Frank is quite close to Van Cleef's Angel Eyes, but perhaps a little more subdued. Wallach's Tuco is much more primitive than Robards' Cheyenne.

Despite the differences, the two sets of characters are clearly based on the same archetypes. The set from OUaTitW are a refined, more mature version of the over-the-top comic book versions from TGBTU. I wonder if in the early stages, Leone planned to film this using the trio from that movie in the lead roles?