Composer Ennio Morricone spoofs his own earlier Sergio Leone-helmed "Man with No Name" film scores with an over-the-top soundtrack, including shrill choral voices and a warbling whistle interwoven with a tinny recurring passage from Richard Wagner's "Ride of the Valkyries". Also the soundtrack reuses part of "Frank"'s theme from Once Upon a Time in the West (1968) for the shootout sequence.
Other familiar actors known for their work in Westerns that appeared in the film were R.G. Armstrong ( Zane Grey Theater (1956), Have Gun - Will Travel (1957), The Rifleman (1958), and The Tall Man (1960) and Leo Gordon (Hondo (1953), Ten Wanted Men (1955), and Santa Fe Passage (1955)).
Jack came to the cemetery looking for his brother the Nevada Kid. The Kid's tombstone read he died in April 1898. Jack says it is June 3, 1899, so the Kid had been dead for over a year by the time Jack got to the cemetery.
One of the headmen of the "Wild Bunch" gang carries a "Mare's Leg" firearm, in a tribute to the Western series, Wanted: Dead or Alive (1958-1961), in which Steve McQueen's bounty hunter used as a main weapon.
The bar scene with the shootout game had Neil Summers as Squirrel, who was a stuntman and appeared in many Westerns in bit parts. He also appeared in The Life and Times of Judge Roy Bean (1972). Steve Kanaly (as the false barber) also appeared in The Life and Times of Judge Roy Bean (1972). Geoffrey Lewis (as the leader of the Wild Bunch) was also in many Westerns. He was in The Culpepper Cattle Co. (1972), High Plains Drifter (1973), Bad Company (1972), The High Chaparral (1970 episode), Shoot the Sun Down (1978), and Tom Horn (1980).