I would recommend against the B Square mount. I used it on my Python and it really damaged the finish on the gun where it "clamps" ie. in front of the cylinder. Ask yourself why you need the scope. The main selling point of the B Square is no drilling and tapping. You use the same screw holes as the rear sight. This is a selling point if you plan on putting on and taking off the mount frequently. In my case, and I have an older model 629, my scope is on (drilled and tapped) and has never come off! I suspect that I have a stronger mount as well.
Peter.

I have a B-Square mount that I had on my S&W 29 w/ an 8 3/8s barrel. As I remember, the pistol was a 29-2 that I bought new in 1987(?). I mounted a Leupold 2X to it cause I was tired of hauling around a rifle while deer hunting in Prince William Sound. Anyway, it mounted with no modifications. The pistol left but the mount stayed around, if it would help you out. Greg