I spray glued a proper scaled plot of the firewall onto some 1/4 inch masonite to use as a router template for the 1/4 inch birtch plywood firewall and later for the metal firewall to be installed over it. I am still trying to figure out what to do with the bottom of the firewall. I am using the Melville cowling which results in a flat shape all the way to firwall bottom edge. That requires moving the firewall edge down something like four inches. That is it for now, still figuring on this one...
