Custer of the West marked Cinerama Releasing Corp.’s debut release, as noted in the 29 Mar 1967 Var. The project was initially titled The Last Trumpet, according to various contemporary sources including the 27 Apr 1966 Var. Other working titles included A Good Day for Fighting, Custer, and Custer’s West. Although Julian Halevy was given co-credit for the screenplay when the film initially opened, according to official WGA records, Halevy was a pseudonym for writer Julian Zimet. The WGA changed the screenplay credit to read: "Screenplay by Bernard Gordon and Julian Zimet."
       Principal photography took place in Spain, and was completed in twelve weeks, ending in Dec 1966, the 11 Jan 1967 Var reported. To reduce shooting time, producer Philip Yordan had organized separate filming units, as stated in the 25 Oct 1966 DV, which identified Robert Siodmak as chief director, aided by Irving Lerner, Noel Howard, and Jack Willoughby. Lerner was ultimately credited as executive producer and director of civil war sequences, and Howard as second unit director; however, Willoughby was not credited onscreen.
       Actor Robert Palmer (a.k.a. Boyd Holister) was cast in the film, as noted in the 9 Jul 1966 LAT.
       By early Jan 1967, scoring was underway at Shepperton Studio Centre in Shepperton, England. Other post-production was set to take place at Pinewood Studios in London, England, the 11 Jan 1967 Var stated.
       The picture was scheduled to debut as an out-of-competition entry on the last night of the Cannes Film Festival, according to an article in the 29 Mar 1967 Var. However, the 9 May 1967 DV later reported that a print would not be ready by that time, and therefore the picture had been pulled. Distribution rights had not yet been acquired, although Metro-Goldwyn-Mayer (MGM) was reportedly interested. Cinerama ended up releasing the film on its own, after receiving joint financing from the American Broadcasting Company (ABC), which, in summer 1967, took a fifty-percent interest in Custer of the West and Cinerama’s other unreleased feature film, Krakatoa, East of Java (1968, see entry), as stated in a 16 Aug 1967 Var article. ABC’s total investment in both films was reported in the 24 Jan 1968 Var as $4 million.
       A news brief in the 4 Oct 1967 Var announced that Custer of the West would have its premiere in London on 9 Nov 1967. A review in the 15 Nov 1967 Var indicated that the event had taken place two days earlier than initially planned, on 7 Nov 1967. In the U.S., the film first opened as a 70mm roadshow release on 24 Jan 1968 in Dallas and Houston, TX. The 6 Dec 1967 Var indicated that it would open as a “hard-ticket” roadshow presentation in only twelve-to-fifteen markets, to be followed by 35mm releases in Jul and Aug 1968. Nearly four months after the Dallas and Houston openings, a 15 May 1968 Var brief described the roadshow series of openings as “generally unsuccessful.”
       Charles Reno, identified in a 3 Oct 1968 DV item as the grandnephew of Major Marcus Alfred Reno, filed a $25 million libel lawsuit against Security Pictures and Cinerama for portraying his deceased relative “as a ‘coward, as a drunkard, as a traitor, as a criminal and as a murderer.’” Maj. Marcus Reno, who was portrayed by Ty Hardin in the film, had been cashiered from the U.S. Army for dishonorable behavior, including excessive drinking and voyeurism, but a May 1967 decision had reversed his dishonorable discharge as “excessive and therefore unjust.” Filmmakers had reportedly not had time to “take advantage of Army’s new judgment.” Charles Reno’s case was dismissed by the Manhattan Supreme Court on the grounds that “libel or slander upon the memory of a deceased person, not reflecting upon his relative, does not give rise to a cause of action for defamation,” as stated in the 20 Mar 1969 DV.