rockheadsguy, Dremel makes a good countersink bit for their rotary tool. The carbon may make it dull after a few times, but it will work very well if you use a screw to test for flush after each pass...
Jim, thanks for the tip. I'm still a little surprised that the chassis would show up with a countersink missing, but it was an easy fix and I can't tell the difference between the one I made and the factory screw holes...
Brian