Not just about the role of Frank, Groggy. Is there evidence that Leone EVER thought of Wayne for ANY part in one of his movies. I'm guessing "no."
No, but I was addressing this specific RUMOR. Wayne hated Leone's films...
Wayne would have been interesting in the role, perhaps more so than Fonda (who was imo a good actor at a nuts-and-bolts level but incredibly BORING to watch, and only got more BORING the longer Leone trained his camera on him),
and Wayne was in general good in darkish roles, but pretty much stopped playing dark after Liberty Valance.
I don't know that we can know if Leone ever thought of him for the part. Even Leone's memory could be faulty at times-he could get turned around on historical details, like describing an incident that happened to Bat Masterson and saying it happened to Wyatt Earp.
And Eli Wallach has apparently denied ever having been approached to play Tuco in Once.
If I were casting Once, I think I would've aged Clint up a bit and made him Frank-that would have really shocked filmgoers who thought they knew what to expect from a Leone film-and maybe cast LVC as either Morton or Cheyenne