I have foun too that any grip that fits a regular new model blackhawk will fit a new model single si except for the new ones just putout by Ruger with smaller grips(shorter)
I too have pachmayrs on my custom 41 magnum as its a beast to shoot otherwise. I hope to get a set of hogue monogrips(rubber) on it when I find them(I have a set around here somewhere). I think they look better than the pachmayr on the blackhawk and help cusion recoil just as well, we will see. If I can buy a set of oversized walnut I may try them as they seem to work on my 5.5 44 magnum Blackhawk, we will see. For no thats how it stands.
Jim L