As demonstrated by Bob Mica at Jeff Schultz' Firewall Forward seminar in Lee's Summit, used a 3/16" drill bit to open up the area on the AeroVee's cylinder head in the central area between cylinders. The starboard head had a small space, however the port side was completely closed off by casting flash. Drilled a series of increasingly larger holes in the area trying to overlap holes, using the side of the bit to 'mill' between holes. Used a medium thickness flat file to smooth sharp area between holes. Drill chuck marred the ends of the cooling fins adjacent to the central space.