Western from Monty Hellman.
Gunman escapes hanging by accepting an assignment to kill a man (make way for the railroads). Starts to like the guy, doesn't want to kill him. Wife seduces him. Fight with husband, they run away. Haunted down, He escapes, she has to go back to her house where more railroads killers await them. Gunman helps them to kill them all, then leaves.
Amusing enough, though I certainly cannot see the "strange amalgamtion of Italian and American western". Characters well-developed? For a western, yes. In general, not particularly.
