I just went through my file folder for the film. The Italian poster "5000 dollari sull'asso" lists in oder Robert Wood, Fernando Sancho, Jack Stewart (supposedly an alias for Giacomo Rossi Stuart), Norman Preston (supposedly and alias for Lorenzo Robledo), Maria Sevalt, Helmut Schmit.
The Spanish poster "Pistoleros de Arizona" lists in order Robert Woods, Fernando Sancho, Helmut Schmidt, Maria Sabalt, A. Molino Rojo
I have a German pressbook which lists in the credits David - Jack Stewart
I have a full set of German lobby cards. I see no one who looks like Robledo and the only person who resembles Giacomo Rossi-Stuart is a scen where Woods standing behind a poker player with three players in front of him. The player on the left is a blonde but I can only see a profile. This is the only actor I can see who resembles Stuart.
I hope this may help.