My gauges require 3 5/32" (80mm) holes for the speedo and tach, and 2 1/16" for the four small ones. The big one is an off-size for hole saws, and the little one is a bit hard to find. They're going into a fiberglass dash. Is it best to cut a 2" and 3 1/8" and then sand up the extra 1/16"-1/32"? Any special type of saw to ensure no problems?