ALL the Blackhawks, and the Single Six have the same gripframe. The Vaquero is steel, but the same size, the BH and Single sixes are aluminum and the same size. All the stainless guns gripframes are, of course, stainless steel. The only different sized gripframes Ruger makes are the Super Blackhawk (longer), the Birdhead (shorter) and the Bisley (different).
The mounting screw location is identical in all, so any gripframe will fit any gun, with the exception that changing to the Bisley gripframe will require changing the hammer and trigger as well. Of course, the birdhead and Bisley are New Model, but the aftermarket standard gripframes (see Brownells or Gun Parts Inc) can often be used for both with some creative modification, like making an old model trigger spring block for the New Model trigger cut, or ordered as an Old Model style.
As the Ruger Old Army has the 3-screw gripframe, broaden your search to include even newly made Old Armies, the blue ones are aluminum. I installed Stainless ROA SS gripframes on 3 screw 357's and they come out great, and the SS gripframe frame looks good on a blued gun.
