As poste above they are interchangeable with two simple caveats.
A. INTERCHAGEABILITY OF GRIP FRAMES:
In general: all Ruger SA grip frames including SBH Dragoon, Blackhawk, Single Six, Old Army, Bisley and Birdshead (excluding Bearcats of course) will interchange from the standpoint of the screw pattern from Single Six to Super BH, Old Model to New Model, and even NM to OM.
All the screws (but excluding Bisley grip), springs and pins can be transferred over from existing GF. Including those with internal locks, but not the lock itself and a standard spring seat is needed.
1. Grip Frame Projections shown here pointing to the right just above the two rear trigger guard screws and both sides of where the hammer would be. To fit grip frames with projections to guns w/o the cut out in the cyl frame, just saw or grind off the projections, they are not needed on steel grip frames:
Photo by G2.
2. Reverse Indexing Pawl System: All the NM FT Blackhawks and NEW Vaqs have this system which allows the cyl to roll backwards enough and stop for the chambers to align to the loading gate trough without the hammer on half cock (which can’t be done on standard new models).
Grip frames from models w/o this system need a divot cut above the trigger guard for the free spin cyl pawl.
Ruger free spin pawl on the right:
Divot for free spin pawl on NM Flat Tops and New Vaqueros with the reverse indexing pawl system shown on the left:
Cutting the divot: To locate this notch, take a measurement from the location on your original GF. Or mark that area on the replacement GF with a magic marker, assemble the GF to the gun, then cock the hammer a few times. This will leave a ‘witness’ mark in the marker ink, so you simply make the "divot" there. Be cautious not to let the cut extend to the outside edge of the grip frame or it will show when assembled, and don’t cut notch too deep!
Use a thin cut-off blade in a Dremel tool. With grip frame in a vice, and your old grip frame nearby for reference, hold the Dremel with two hands for control. And replicate the divot in the new grip frame. It’s easier to clamp the Dremel tool in the vice at an angle and hold the grip frame instead.