The film's English dub is the first, and one of a select few, in which Bud Spencer provides his own voice. In fact, this was one of the rarest examples of spaghetti westerns and earlier films with Bud Spencer to provide on-set sync sound recording instead of usual post-dubbing technique which was a common thing for Italian films.
Don Taylor did not complete "Five Man Army". It was probably finished by either Dario Argento or Giulio Questi.
Tetsurô Tanba who played Samurai was forced by the director to wear Chinese-style hair and costume. He refused, but this was not accepted. He became angry and was preparing to return to Japan and finally the director withdrew the request.
In addition to writing the screenplay, Dario Argento directed some of the scenes uncredited. This was before his official directorial debut the following year with The Bird with the Crystal Plumage (1970).