Neither have I. If I’m not mistaken, there are only five white/Caucasian/non-Japanese characters in the entire film: the three cutthroats at the beginning, “the American” played by Lloyd Battista, and Anthony’s Stranger. Neither the German nor the English opening and closing credits mention any other actors besides those two and the Japanese cast.
The first one of the three bandits could be Gaetano Scala.
There is a second extensive thread on Lo straniero di silenzio, where @Squonkamatic wrote years ago, “Tony Anthony […] even managed to find a little part for Raf Balda[s]sarre.” I also wonder what the source is for the information that Raf Baldassarre’s character is called White-Eye. Help! Who knows more about this? Maybe @Carlos and @JonathanCorbett?