You pegged it Ferrara, M.C. Horses has to be my all-time favorite western song, though it is modern. The Old Double Diamond is right up there with it and is actually easier to do (and sounds better) for soloing on guitar. M.C. Horses sounds best when Tyson has his fiddle player involved.

Though I'm repeating from some above, other really good ones are
Old Paint (or Leavin' Cheyenne as it's sometimes called), Windy Bill, Darcy Farrow, Murder Steer (another Ian Tyson song), Whoopee Ti Yi Yo, Night Rider's Lament, and Home on the Range (when it's done almost like a hymn the way Tyson did it). Another one I like because of the movie it's in (Rio Bravo) is My Pony, My Rifle and Me.

Come to think of it...I'm such a big Ian Tyson fan that everything western he does is good.

SC