I thought about that too, but I haven't found any proof of it. All I know, is that the second Italian producer wanted both Hill and Buccella in the cast, and asked for more western influences. But then again, it might have been easier to sell the film in Spain as a sort of 'spaghetti western'. Franco wasn't really a fan of Proudhon, as far as I know.
Watching this movie, you notice that Camus is no Saura, like you said.
Still it's a film worth watching