Here is the low down on "new model" Ruger SA grip frames.
XR3-RED grip frames have round trigger guards.
"Dragoon" style grip frames have square backed trigger guards.
The new model "blued" blackhawks and single sixes have XR3-RED "black" aluminum grip frames and ejector rod housings. (see note below about ejector rod housings)
The new model "stainless" blackhawks and single sixes have XR3-RED stainless steel grip frames and ejector rod housings.
The new model "blued and stainless" Super Blackhawks have steel grip frames (blued or stainless). The 4 5/8" (unfluted cylinder) and the 5 1/2" (fluted cylinder) Super Blackhawks have the XR3-Red STEEL grip frames with round trigger guards and the 7 1/2" (unfluted) and 10 1/2" (unfluted) Super Blackhawks have the square back trigger guard "dragoon" style grip frames. The Ejector rod housings are aluminum on the blued models and steel on the stainless models. (see note below about ejector rod housings)
The Super Blackhawk Hunter model has the larger "dragoon" style grip frame BUT has a round trigger guard (Only on this model). This grip frame takes the same grip panels as the "dragoon" style grip frames.
The Vaquero models have steel grip frames and ejector rod housings on all the new models, blued or stainless. Some older blued Vaqueros have aluminum ejector rod housings on the blued models. (see note below about ejector rod housings)
Now the XR3-RED and the Dragoon style grip frames are interchangable on the guns, but have different grip panels. Now ruger has the smaller (not birdshead) grip frames on the new "vaquero style" .32mag single sixes. And the the birdshead frames on the vaqueros and single sixes.
NOTE: all new centerfire single action guns are shipping with steel ejector rod housings. (per the Ruger 2002 catalog)
Bisley grip frames are steel and can be added to any of the Ruger SA guns with minor modifications.
As far as I know Ruger will selll you any of the grip frames they make, but the steel models come unfinished.