The homestead encountered when the group leave the train (at 43 minutes) is the same as the McBain homestead in Once Upon A Time In The West (1968)
Also went by the title "Massacre at Fort Holman"
The prison set from John Guillermin's " El Condor " was re-used during the filming.
Composer Riz Ortolani uses almost exactly the same instrumentation, musical key signatures, and musical cues in parts of this film as he did in Day of Anger (1967), which is also directed by Tonino Valerii.
Due to the massive TV success of Telly Savalas as Kojak on the BBC, this was released in the UK and Ireland with a huge TV advertising campaign, which would have been very rare at the time.