I’ll edit the database with regard to Juan Fairen and Sergio Aparici then.
There is one more guy who is in both Death Played the Flute and A Rope at Dawn. Here he is as the sheriff’s deputy in A Rope at Dawn:
This seems to be the same guy as the sheriff in Death Played the Flute, and in exactly the same outfit:
I have no clue as to who this is.
Buy the way, it seems there is a different guy playing the sheriff in the later scenes of Death Played the Flute (together with Michele Branca), probably an Italian actor: