The Stovebolt Site Forums The Shop Area Paint and Body Shop Heater motor to firewall seal

I'm with Brad Allen on this, your motor is non-stock, from the looks of it, the motor barely protrudes out past the firewall.
The stock motor sticks out past the firewall, which gives you the ability to slide a gasket around the motor housing to make a seal.
With the motor you have, it could be covered with a round metal plate. You would have to cut off the access screw threads.
Original Posters Picture of Heater Motor
It is kind of hard, to tell, just how far the motor sticks out past the firewall, because of the angle the picture was taken.