In 1969, Altman was in post-production on "M*A*S*H" and sneaked Foster into the screening; Foster liked the film, and signed Altman to direct a film based on "McCabe". They agreed to wait until "M*A*S*H" became a box-office hit to take the pitch for "McCabe" to a studio for funding. A second screenplay – independent of Maddow's – was commissioned from Brian McKay, who completed it in only five weeks. A revised version of that screenplay dated July 1970 became the "shooting script" for the film. Altman and McKay are listed in the film's credits as its screenwriters; Maddow went uncredited.