If the timing is such that the screw is turned past where it should be and past where it was originally, someone has likely overtorqued it, buggered the threads, and you should not remove metal from anything anywhere. Instead make some very very thin washers out of brass shim material or even of aluminum can material and put them under the screw head until you're where you want to be. You can thin a washer in increments and eventually get it to where you want it. If the timing is such that the screw is short of proper timing and from where it was originally, it could be that the screw has been put back into the wrong hole. That happens to a lot of vintage Parkers.
