I think it was actually Bill Elm (the other RDR composer) who was in FoDM! I’m a huge fan of their work on this. There’s a great video put out by Rockstar about their approach to voices, timbre, and layers on the soundtrack:
I love this album, and had no idea it was a movie as well! Thank you!
Check out Enya’s Spaghetti Western Theme from the Celts. It is available on her Amarantine EP. I know it seems incongruous, but it is a great song and it effectively evokes Morricone’s use of bells, guitar, and soaring vocals.
Another group that I did not see mentioned is Dead Combo. They are from Lisbon. There are clear influences from Morricone and Spaghetti Western soundtracks.
Check out their songs “Mr. Eastwood” and “Mr. Leone.” Cheers.