See Peep and Firesights and Long Range Sights in the FAQs, the Williams WGRS, FP and FP-TK are bolt ons, mount in the two rear scope mount holes, I have the FP-TK on my 45-120 BC. If you want to get the most range out of a globe front sight, you'll be wise to swap out for a lower sight, the .404" tall 17A Lyman will get you out to about 800yds with the FP-TK rear sight, shooting trapdoor equivilent 405gr loads(1400fps) with the rear sight at the bottom, POI is about 1½ high at 100yds in my 45-120 using the .404" sight, I haven't shot past 200yds, but Bernie has used his with 500gr Lee 500r bullets at 1500fps out to 800 meters.
Tim