The Williams WGRS mounts in the back two scope mount holes just ahead of the hammer. Works great!
This sight is ramp type with an aperture. They were available for less than $25 from the old H&R/NEF, not sure if the new Big Green still has them available or not. Most other places they run in the $35 ball park, I think mine was $22 a few years ago from H&R/NEF.
You can use it with the aperture installed, or unscrew it and use it as a ghost ring.
