Uh, that's XR3-RED. It's the grip frame. Used on old model Blackhawk, Single Six, Super Single Six, Hawkeye and Old Army. The stainless ROA grip frame was identical but marked as KXR3.
Redesigned in 1973 for new model trigger springs and transfer bar, called XRN-3RED. Same dimensions as XR3-RED. Used on new model Single Six, Super Single Six, Blackhawk, Vaquero and some Super Blackhawks.
The grip frame really doesn't impact many action parts, except of course the main spring and trigger springs. However, 4V50 Gary is correct about there being many common parts between the ROA and other Ruger SA guns.
Also, the ROA did not incorporate the transfer bar (as 4V50 Gary stated) nor the new trigger spring in 1973. Thus the XRN-3RED grip frame is NOT usable on an ROA despite being dimensionally identical.
If you'd like a little extra credit homework assignment, read and attempt to comprehend the Ruger SA revolver grip frame history in:
http://www.gunblast.com/Hamm_Ruger-SA-GripFrames.htm