Many moons ago I compiled this list with the late Kent Johnson: it was a proposition for an anthology with Western stories by authors known mainly for their science fiction / fantasy / horror. We never read any of the stories (unless Kent did), so we didn't take this very seriously, but we called the list The Mammoth Book of Western Stories by Science Fiction Authors. Almost all the stories are from pulp magazines, with the possible exception of Moorcock's story, which is almost surely juvenile. I think this still sounds fascinating. EDIT: I found the date for Moorcock!
Robert Bloch: Chinaman's Chance, Mammoth Western, August 1950
Fredric Brown: The Stranger from Trouble Valley, Western Short Stories, November 1940
Lester Del Rey: Justice Rides the Winds, April 1949
Gordon Dickson: Practice Makes Perfect, Texas Western, July 1953
Harlan Ellison: The End of the Time of Leinard, Famous Western, April 1958
Gardner Fox: The Killer in Johnny Kidd, Western Magazine Mar 1956
John Jakes: The Gun-Doc of Hangman's Gap!, Max Brand's Western Magazine, January 1953
Will Jenkins: Shootout, Ranch Romances, September 1957
Damon Knight: Scattergun Guts, .44 Western, September 1948
Michael Moorcock: Johnny Lonesome Comes to Town, The Searchlight Book for Boys, 1956
Emil Petaja: Cure-All for Coyotes, Western Aces March 1946
Robert Silverberg: Walkdown, Western Action, November 1956
Clifford Simak: Gunsmoke Interlude, 10 Story Western, October 1952
Theodore Sturgeon: Scars, Zane Grey’s Western Magazine, May 1949
V. E. Thiessen: The Barber of Buffalo Bend, Ranch Romances, September 10, 1954
Bryce Walton: High Road to Hell, Triple Western, April 1953
A.E. van Vogt: Ride in Killer, Famous Western, February 1951
