Some commercial rifles have a pair of drilled and tapped holes on the left side of the action for a Williams. Holes would be 5/8" apart, as I recall.
Williams also makes sights to mount on the scope holes on the top of the rifle. If the rifle has holes ready to take the Williams sight, it is a real easy thing to do. Otherwise the rifle will probably need two holes drilled. Not a big deal.
One suggestion. If a rifle with a Williams sight is propped up againt a car, tree, cabinet, etc and falls over, the bridge is easily bent. Be careful.