Heater door placement in firewall for Otwell heater

[1crosscut]

So I have an Otwell heater that I would like to install on my 29 AA. I put it on my truck today to see how it would line up with the firewall and it would require the hole to be cut on an area of the firewall that is an outside corner.
The same thing is true if I were to use a cover that fits over the standard manifold.
I cut a partial piece of aluminum flat stock to better show where it would require the hole to be cut if coming directly out of the heater outlet.
Is there a special heater door for this? To cut the hole in a flat area of the firewall would require a flexible tube and it would be hard pressed to make the bend necessary to connect it to the heater door.
Suggestions?