If memory serves, Melvin Tyler pictured a square butt snub M-19 on his grip adaptor boxes. He probably had a square butt gun re-barelled.
I can see round-butting a M-66 or 19 to get a four-inch round butt gun. Never had any desire to have a sq. butt snub.
The sq. butt J-frames have a somewhat rounded butt, not too bad. I had a M-36 with three-inch bbl., factory Magna smooth rosewood grrips and the Tyler adaptor. Nice gun that I regret having had to sell. Yes, I salvaged the grips when I sold it and no, they aren't for sale. I hope to find the stainless equivalent M-60 and put the grips on it. They're around, occasionally. I once owned one. (My M-60-4 has a round butt and wears Pachmayr Presentation Compac grips.)