Do not lower the tumbler notch. That could cause the sear to strike the safety notch when you fire the gun, unless you have a fly in the tumbler. Even then, bad idea, because the fly can cause a hang up then. First lighten the sear spring. It only needs enough strength to return the sear in a safe and positive mode. Check your progress using the safety notch. Using 60/40 lead solder, solder a small steel plate behind the tumbler notch, that is thick enough to be roughly even with the top edge of the notch. leave a small gap between the notch face and the plate. Then file the plate down until the full face of the sear will engage the notch. No more than that. Do this proceedure after polishing everything that moves against another surface, and polish that surface. That will give you a very good trigger pull as long as angles were correct to start with. 98% of sear springs are way over powered, most need only a third of that power, and often less. If you find the trigger to light to control afterwards, then file a little more off the plate. The nice thing about the plate, is that it can always be removed, leaving things just as they were. The 60/40 solder flows at 375° and that heat will not affect the tumblers heat treat if you are careful to not over heat when you solder. If you are not good at soldering, use J&B WELD to secure the plate. Using this method, will usually bring any trigger down to a very nice pull, as long as contact angles are reasonably correct. I can normally bring double lever set triggers down to 2lbs, when unset, by doing this.