Premise: Gunfighters of Casa Grande (Spanish: "Los Pistoleros de Casa Grande" ) is a 1964 Eurowestern film, co-produced by American and Spanish producers. Based on a story by Borden and Patricia Chase, it was later developed into a screenplay with the assistance of screenwriter Clark Reynolds and directed by Roy Rowland, the last film he made for Metro-Goldwyn-Mayer.
Hypothesis: Clark Reynolds has written many Eurowesterns.