Trigger pressure in a Smith is primarily determined by the rebound spring, reducing this to a 12 or 13 pound version will get you down to your desired release weight. Polishing the sliding surfaces of the rebound block, the sides of the hammer and trigger and the bolt will smooth it up. Under NO circumstances should you attempt to stone the hammer notch, and the trigger engagement edge is only to be changed in rare circumstances. The strain screw is something that seems to be an easy way to lower trigger weight BUT this is only useful if double action is the main use pattern. Backing the strain screw out lowers torque on the hammer and thus it gets slower - not what you want if SA is the main use, in which case all the way in is best. A crisp trigger will feel the same whether it is two or four pounds. If your intent is ISSF centrefire the rule specs one kilo lift, I always try for two and a half, but I have had triggers that I swore would not lift a pound, but they in fact lifted three and a half. Don't try to push the rules, a good trigger is better than one that is marginal but erratic in pull. Don't obsess over the weight, just make it "good".
Dr Jim