Step one for the cowling was to cut out a 130mm circle in the front of the cowling to keep it from touching the propeller shaft. To do this, I enscribed a 65mm radius circle on each half of the cowling (upper and lower) centered on where they overlap. I then rough cut the fiberglass to something resembling the final opening. Then using a grinder fitting on my electric drill, I ran the opening out to the inscribed line. Finally, I used a sanding drum on my dremel to smooth out the opening.
130mm semi-circle drawn onto lower cowl centered on the raised lip.
Rough cut out of 130mm semi-circle on upper cowl.
Upper cowl with prop shaft circle cut out and cleaned up (sanded).