The original Ruger Blackhawk "XR3" Aluminum grip frame, used from 1956 to 1962, is very similar to the Colt SAA grip frame. Ruger changed the Blackhawk grip frame to their "XR3-Red" design in 1962/63. The XR3-Red grip frame allowes a little more room behind the trigger guard. Starting in about 2004/05, the Ruger "New Vaquero" and the 50th anniversary New Model flat top Blackhawks were introduced (In both the large frame 44mag, and the small frame 357mag). These models were given an all-steel XR3 grip frame. In the last few years, Ruger has also produced Small frame flat tops in 44 special and 45 Colt, both using the steel XR3 grip frame.
Personally, I love the XR3 grip. It fits me much better than the XR3-Red. However, the steel XR3 grip frames make for a pretty heavy "packing pistols". The old model and OM flat top 357's with 4 5/8" barrels converted to 44 special weigh about 34 ounces. Similarly configured New Model 44 specials with the steel XR3 weigh 41 ounces, or so.
A small company in Misourri called Grand Masters LLC (formerly Power Custom), is making two piece steel XR3/colt SAA style grip frames for all generations of Blackhawks ($200). Last week, I sent them an email, asking them if they could produce a run of aluminum XR3 parts. They haven't got back to me, but I'm not giving up yet. If you would like to see this part produced, contact Grand Masters with a real commitment to buy one, should they decide to produce them.

email@powercustom.com
573-372-5684

Thanks,
Matt

I spoke with Randal Power on the phone yesterday. He would need a minimum order of close to 50 to motivate him to make a run of these. He told me he could sell them for $150-$200 a piece.