Best "trick" when removing the three trigger plate screws from any Parker- (1) have the properly ground to fit screw drivers- seat the receiver bottom up in a well-padded vise-- make a drawing on paper- I mark the rearmost screw (near the trigger guard bow as No. 1- the left barrel side screw as No. 2 and finally the right barrel side screw as No. 3- And I turn each screw out a little bit, and then go to the next one in 1-2-3 order, rather than taking say no. 1 all the way out, then 2, then 3- this equalizes any binding pressure on the trigger plate- then I remove the rear tang screw and finally the top (under the lever) tang screw that bottoms into the front trigger block--
I tape each screw to the proper number on the tracing paper- those Screws are Not Interchangeable--
A friend came over with a sweet GHE 20- about 1912 mfg-older DHBP with the spur inset into the stock heel- but the two original engraved head Fillister type butt plate screws didn't aling slot to slot as they should have, and they didn't "bottom" in the counterbored holes in the black bakelite BP-- simple solution- someone had at one time removed the BP and reversed the two screws- so I 're-reversed them" and they 'clocked" perfectly and set just a hair below flush in the counterbored holes-- lucked out on that one- whenever you can avoid regrinding or filing under the head of an original screw, that is a good thing--