I decided on an upper and lower firewall pass thru for wiring. I am using Avery Tools stainless steel firewall pass thrus. Marked locations and drilled center with #40, then used step drills to increase hole size to 1 1/16 inch for both. Deburred center hole then used the flange as a drill guide for the mounting holes. Marked center with #19, then drilled through with #40 and upsized to #19. Did one hole, inserted bolt and used non-locking nut to snug it down. Repeated for other three mounting holes, inserting screws and nuts as I went. Removed flange and deburred all holes. Assembled flange and coverplate per instructions and tightened lock nuts.
