What makes the film distinctive are two things. Firstly some of the story elements are unusually dark for a standard Western (the script is by A.S. Fleischman from his own book but I have no idea if anything was contributed by Peckinpah), Thus Turk is a crazy Confederate deserter who once tried to scalp Keith’s character and who dreams of setting up his own state (rather unfortunately called Freedonia the same name given to Rufus T. Firefly’s dominion in the Marx Bros' Duck Soup, 1933) run with Indian slaves; Yellowleg is scarred physically and psychologically and bitterly set on revenge; there’s the dead child; and an attempted rape of Kit by Billy. Secondly, Peckinpah’s directorial hand, aided by cinematographer William Clothier, is quite evident is giving the otherwise quite standard production its grit although as the film was produced by Maureen O'Hara's brother, Charles B. Fitzsimons and O'Hara and Brian Keith were fresh from co-starring in the box-office success of Disney's The Parent Trap released earlier the same year, he was presumably hired as jobbing director.
Apparently O'Hara did not like his style (rather bizarrely though Peckinpah manages to get her clothes off in two scenes) and indeed the film was eventually taken from him, something which presumably explains the film’s rather twee and anti-climactic ending. The Deadly Companions will be of most interest to Peckinpah buffs but as Western it is solid enough fare.