DON'T start filing or stoning until you are sure it is needed.
I will probably get in trouble again for heresy, but I like to remove the internal parts and just install the safety alone. This makes sure it fits, that it interfaces with the plunger OK and that it locks into the frame properly when in the up and down postions.
Then install the internal parts and install the safety. Try to set it to the ON (upward position). If it goes up OK, try to pull the trigger. Any sear movement is not good; you may have to try a new sear.
If it won't engage the sear (you can't move it to the ON position - the normal condition for a new safety), stone carefully on the engagement surface. This is a cut and try proposition, so be patient. You may need to install and remove the safety a half dozen times but better to take off too little metal than too much. (To make the job easier, you might want to remove the safety spring and the plungers from the spring tube, so you don't have to fight the plunger every time you install the safety. Remember, you already checked that interface.)
Jim
Jim