Well, not in Viet Nam but there is an interesting picture in the new Ruger Pistols & Revolver book by John C. Dougan. It's a couple of Marines in Santo Domingo, Dominican Republic dated 5/13/65. They are seeking out a sniper, and one has a Ruger 6 1/2" .357 Blackhawk in his hand. You can't see what type of holster he was using unfortunately.