With the holes cut into the firewall, I began installing the flanged pass-thru port for the heater. I accomplished this by marking and drilling 6 pilot holes into the firewall side, hose attach flange for future rivets. Next, I used the hose attach piece as a template to drill holes through the firewall. Finally, I clamped the firewall side piece flange to the cockpit piece flange as a template to drill the cockpit side flange. With all three pieces (2 x pass-though pieces and a firewall) pre-drilled, I clecoed them in place to test fit/alignment and to see if the butterfly valve still rotates freely. It does.
Test install of the passenger side heater hose attach point.
Inside the cockpit view of the temporarily installed butterfly valve.
