Dust Devil, maybe I'm misreading your posts above but I just want to clarify that track 5 is comprised of 2 separate soundtracks. You're right the first 46 seconds of the track are used when Tuco is crossing the rope bridge and ends when Tuco reaches the water trough. However, the remaining 1:05 of track 5 is not used in any available cut of the film. My guess is that it was intended for the Socorro sequence.
So, yeah, it is possible it was intended to be used in the S scene, but without any sort of hint pointing in that direction, we're really shooting the breeze here.
Yeah, it's only speculation and we'll never know for sure unless The Leone Family comes forward with new revelations about any lost/deleted scenes.
I have a hunch this unused music was for the Socorro scene for 2 reasons:1) If we can reasonably assume that the Socorro and cannon duel were the only 2 scenes deleted (aside from the grotto scene that has found its way back into the MGM extended cut), then the more playful feel of track 5 is consistent with the happenings of the Socorro sequence (i.e. Blondie having a laugh at Tuco's expense) but obviously not the cannon duel.2) Consistent with Track 3 grouping the soundtracks of 2 scenes where Sentenza kills Baker and roughs up the fresh young whore Maria, Track 5 groups Tuco's post-desert rope bridge scene with this mystery music.