Following SW are inspired by biblical stories:
Per 100,000 dollari ti ammazzo (Vengeance Is Mine aka Django der Bastard): "it tells a Cain and Abel story of two half brothers, one good, one bad..."
Mille dollari sul nero (Blood at Sundown aka "Sartana"): "Cain and Abel"
E dio disse a Caino (And God said to Cain aka Satan der Rache): Cain (Acombar) gets punished by the revenge god (Kinski)
Following SW are inspired by greek mythology:
Il ritorno di Ringo (The Return of Ringo aka Ringo kommt zurück): "Gemma plays the Odysseus / Ulysses role"
Il pistolero dell'Ave Maria (The Forgotten Pistolero aka Seine Kugeln pfeifen das Todeslied): "is a retelling of the Greek legend of Orestes"
Following SW are inspired by Shakespeare's plays:
Quella sporca storia nel west (Johnny Hamlet aka Django - Die Totengräber warten schon): "the plot is basically the same as Hamlet"
Dove si spara di più (Fury of Johnny Kid aka Glut der Sonne): "The story is based loosely on Shakespeare's Romeo and Juliet."
Are there any others? ;D