When I converted a few single sixes from plow-handle to the birdhead GF I didn't need a thing extra. However your Midway frame might need some fitting. You might try to locate a Ruger birdhead GF in the Want to buy ads and see what happens. All the Ruger birdhead GFs are the same size whether it be for a Single Six, Vaquero or whatever. I do believe I am correct in this, I've converted 15 or so guns over the past several years using the Ruger GF and have had all the parts and pieces fit.
A Birdshead is nothing but your XR3-RED/ "Plow" that is round butted.
A Bisley Hammer and/ or a Trigger can be used if you seek those particular attributes,,,ie Wide Lower Hammer Spur and extra Curved Trigger,,,
The Bisley hump will need to be removed and some of the Trigger will need a slight trimming.
I personally like the Bisley Hammer, and compare the 2nd gun Trigger to the others to see a Bisley Curved Trigger -vs- Standard.
The rest of the guns have a standard trigger,,,
that I like to thin a bit and remove a good portion of the backside web,,, all in a effort to make the Standard trigger look more streamline,,,IMO the standard Trigger can look "chunky".
Found this picture in one of my old computers, Showing the cut line (Black) on a QPR XR3-RED Brass Gripframe (Gen 2), if one wanted to make it into a Birdshead. the Gen 1 is the frame that is missing all the extra material. (Pictured Right)