As a Colt certified armorer myself and someone who operated a full and part time shop building 1911's for many years, I would take that "book" and throw it in the nearest round file. First, sears and hammers are hardened all the way through. They are not case hardened which is what happens when the surface only is hardened. You may stone both the sear and hammer. One should use stones that are absolutely square on the edges in order to insure that the surfaces are squared and the angles maintained. Most porfessionals use these kind of special stones only for trigger work and they keep them both clean an maintain the integrity of the edges. You also need a total flat surface to work on sears and hammers....most use a flat small pane of glass for that purpose. A jig for sears is very helpful but not required. Tom Wilson used to make special jigs, some of which are now made and sold by Brownells for the purpose. Tom Wilson was a US Air Force armorer at Lackland AFB in San Antonio for the Air Force competition unit. After he retired he was in the business of 1911 competition guns and made tools. He then quit, sold out and went to Arkansas to build Fire Engines. One thing that is know to smiths is that the sear spring has a great deal to do with felt "weight". You can bend the center prong back to reduce weight...a little at a time or bend it forward to increase weight. The left prong can be used to fine tune the pull for about 1/2 lb or so. The right prong functions only on the grip safety and shouldn't be bent. This might be something you might try.
For competition the National match rules required a 4lb minimum for Hardball and 3.5lb minimum for center fire on 1911 pistols. All triggers were weighed at Camp Perry matches to insure that they met the rule. Spring pull gauges are not very accurate. Most professionals use actual steel weights that are calibrated and hang them on the trigger using a heavier center hanger that will allow the weight itself to activate the pull. Weights can be added or removed from the center hanger till the real pull is established. This type of weights can be purchased from many sources including Brownells.