Wainwrightbagger: One other potential approach is to go with a proper target sight (ie Parker Hale) that requires no permanent modification to your No. 4. The standard No. 4 "peep" has a 0.10 inch aperture and is not meant for serious target shooting. I have 3 scoped No. 4's but my best groups shot to date are still with my Parker Hale sighted '43 Longbranch which seems to be "uncannily accurate" (probably due to a pristine post-war 6 groove barrel). You might find you enjoy shooting with one of these target sights- certainly agrees with my 58 year old eyes.
Ridolpho