Great summary be Ale. And a little more detail if interested:
In general: All Ruger SA grip frames will interchange from the standpoint of the screw pattern from single six to Super BH and from Old Model to New Model.
Here are the details to be aware of:
1. Below is a photo of the ears around the base of the hammer. They get taller as the frames get newer. To simplify production in about 1997, Ruger increased the height 1/16” of the cylinder frame mating surfaces on both sides of the hammer to match the Bisley models so they could be assembled to any style grip frame.. Therefore the 'ears' on the standard grip frame had to be made taller as well. So there's basically two sizes: short .530” pre 1997 and tall .590” after 1997. Measured from the very top edge of the grip panel to the top of the ears. That's why it's important that any acquired grip frame match the vintage of your Ruger that you want to put it on. Also, it took Ruger awhile to get the base of the hammer enlarged to match the ears, ca. 2000, in the serial range 56-XXXXX.
2. Pre 2005 steel and all of the aluminum grip frames have two projections just below the ears in the photo above that stick forward into recesses in the Main frame. They can be cut off with no ill effect to fit a newer main frame w/o recesses. If speaking of the new XR3 (slightly smaller Colt size grip frame), that has the Ruger Indexing Pawl (loading gate/chamber alignment system), you'll notice a slight depression above the trig guard on the left side of the grip frame that will need reproducing in any other style swapped grip frame for the alignment system to work; but again another simple task.
3. If your grip frame is an XR3 size (the back of the trigger guard is 3/16" closer to the front grip strap than the grip frames, standard XR3-RED size, SBH Dragoon, etc. The aluminum and same size steel grip frames (are the XR3-RED size) and have the benefit of less knuckle rapping under recoil. You should check out this site for a good explanation and illustrations of the different size grip frames.
http://www.gunblast.com/Hamm_Ruger-SA-GripFrames.htm
4. Just to be aware: the New Model flat top BH & NEW Vaquero XR3 size steel grip frames are 7/16" thick, all other steel and aluminum frames are 1/2" but this does not affect the interchangeability, just the feel in your hand.
5. Many of the recent years NM XR3-RED aluminum and blue XR3 steel have the internal lock except the most current production. The lock can easily be eliminated.
6. New Model grip frames work on Old Model guns with modification for trigger return spring, and visa versa, Old Model grip frames work on New Model guns with modification for trigger return spring and a few extra drilled holes.
