Had a difficult time understanding where the reference datum was located until noticing a half cutout for cowling intake in an alternate view on plan sheet XNB-P13, detail P. Determined the drawing reference line uses the top of the vent to the bottom of the cowling lip distance to be 6-1/2". Rear edge of vent located 2" from the cowling/fuselage seam. Drilled an 1-1/4" hole for the foreward top vent and 1/8" for all others. Used an oscillating tool with wood saw to cut fiberglass.
