A RUGER Bisley Gripframe is Same/Same, be it Blackhawk, SuperBlackhawk, Flattop, Vaquero and Single Six. Same frame across the entire line. (exception; Bearcat)
Only made in New Model configuration, but now days there is a plethora of ways to adapt it to a Old Model.
Midway will have Ruger manufacture. Stainless and Blue, but Blue can be a difficult when it come# to "in stock".
RW Grip frames makes Bisley configuration, in Brass or Aluminum, with all sorts of "Bisley" configurations, standard, jr, fingergroove, potatojudge, Keith to mention a few. RW Gripframe are top notch, high quality, CNC,,, they will initially mount up better than a Ruger.
rwgripframes.com
Either gripframe will take quite a bit on & off/ fitting & finishing, there is no swap it on, unless you buy a frame tha5 is a takeoff, and even then it's fit & finish is a shot in the dark at best.
A Old Model Flattop with Bisley hammer/trigger & Brass Grip Frame.
A New Model Flattop 45/45acp that has had a Birdshead Grip frame swapped on,,,this could have had a Bisley GF with the same amount of effort.
And here is one of the NEW Medium Frame Bisley 41 Magnum, same size as your NM 357 flattop. (Not my gun, stolen picture)