IIRC the old and new model Blackhawks both use the XR3-RED. The change from XR3 to XR3-RED happened when they went from the slightly smaller "flat top" frame, to the larger "Blackhawk" frame, and has nothing to do with being 3 screw or new model.
Someone chime in to confirm if I remember this correctly or if I got it wrong...feeble mind.
Not exactly. The only smaller frame was the .357Mag Blackhawks and that frame size continued until New Model production. The .44Mag flat-top was a large frame with the same grip frame. In 1959, the Super Blackhawk only added the protective rear sight ears, longer "Dragoon" grip frame, wider hammer/trigger and unfluted cylinder.
The change from XR3 to XR3-RED happened in 1962. The XR3 is a dead ringer for the Colt SAA/Navy grip. The RED version just has more room behind the triggerguard. ALL grips of the RED pattern interchange.
