I have this US 3 disc "Man With No Name Trilogy"

I checked the English 5.1 track and the English mono track, and they are clearly DIFFERENT.
The mono track is NOT a mixdown of the surround track.
Some examples
the 5 minute mark where "The Ugly" is introduced, the gunshots and the shattering window sounds.
the 12 minute mark where "The Bad" makes his first kill.
The explosion of the bridge
The sound effects in those are similar sounding to the 2-disc US DVD editions Italian mono track.
So unless someone can correct me, the trilogy set HAS the correct English mono track.