Payment in Blood (1967)

"The battle for victory is ended... but the war for revenge goes on!"

Chamaco finds himself on the wrong end of a firing squad after tracking an ex-Confederate to interrogate him about General Beauregard's missing gold. He's saved by a stranger who calls himself Stuart Byrnes. Stuart claims to know the location of Beauregard's strongbox, and so Chamaco takes him to Blake's camp. After a sort of initiation by the gang, Stuart leads Blake's men back across the border to Durango to retrieve the gold.