replacing plastic panel overlay w/aluminum

I want to make my own aluminum overlays to simply replace the plastic
in my Piper Cherokee. I've been told over and over that this is
cosmetic, non-structural and therefore legal without an approved 337.
The only thing is that on the middle and lower strip of instruments
(fuel guages, RPM, etc.) in the older Piper Cherokees, there are no
screw holes on the surface. The plastic snaps in. i would want to
drill 4 sheet metal screws into those sections of panel. Would a 337
be required for that? My local FSDO (PHL) is very difficult about
things like this, so I don't want to even talk to them. If putting
screw holes in my panel to hold the new aluminum overlays is going to
raise a fuss, I'll think of something else like velcro. on the same
note, I there are other holes in my panel already that were put in for
various reasons (mic/phone/music jacks, avionics master switch, etc.).
None of these things have explicit logs or 337s that say 'drilled
hole in panel'.