S&W won't do the conversion.

Bain & Davis is probably still in business. A buyer of one of my guns used them as their transfer FFL a couple of years ago. I bet they can still do the work.

Quite a few years back, I owned a M-28 so converted. The seller told me B&D did the work but it wasn't marked in any way. It shot quite well, a bit faster than the regular .357 with the same bullets, but at normal handgun ranges I don't know how much difference it would make, in either bullet drop or stopping power, especially in a 6 inch barrel. I thought mine shot flatter at 200 meters, but it might just have been it shot LOUDER!

I had thought about using it for handgun metallic silhouette matches, but at the time, the rules would have put it in a class shooting against trick XP-100's and T/C Contenders.