Measure 6 times... cut/grind once! The advice was to work with the plexiglass and not against it. Compound curves on both the aircraft with even the slightest variations of the surfaces made this a tedious process. Remembering that you can not put back what was ground away I took my sweet time. Shaving and fitting to see how the plexiglass reacted to the last bit of cutting. I used a carbide cutter that also had not only an edge but a face that allowed fine shaving. I combined this with a hand file and a precision motor grinder. I intentionally used low grit so as to not accidentally take away to much material at any one time. Sika and straps with soft insulation blocks to hold in place as the adhesive cured.