Frenchie, that doo-hickie, often called a hammer-block safety, is not adjustable. You don't do anything to that tiny setscrew, that is for installing the pieces. There is linkage that goes down through the hammer to one of the notches. Supposed to keep the hammer from being able to fall unless the trigger is pulled, or something like that.
Actually, Uberti still puts that hammer on Cattleman, as sold by Taylors, Stoeger, etc.