The S&W mounting adaptor uses the 3 mounting holes provided in any adjustable sight revolvers made after 1993. If you have an earlier target sight equipped S&W you'll have to have the top strap tapped to the new pattern. The way this sight mounts is you remove the rear target sight and replace it with the mounting plate for the J Point reflex.

BTW, I've tapped my 67-1 and 617 no dash with the new mounting pattern and the new holes do not interfere with the old mounting hole for the rear sight, however the front hole in the new pattern is close and the tap can hit the rear of the barrel. To keep from hitting the barrel on my guns I shifted the pattern to the rear by 0.03 inch relative to the factory locations on the newer frames.

For a fixed sight revolver the only option would be to machine the top strap to duplicate that on a target sight equipped revolver and then tapping the new pattern in the frame. IMO it's not really a viable option for a revolver with fixed sights, it's going to cost too much and you'll never be able to restore that gun back to it's original appearance.