There are two types of Air Flow heaters one with the door 53-55 1st, and the one without 1947-52. The parts I mentioned are common to both of these Air Flows.
With:
https://www.flickr.com/photos/advance-design_parts_co/8129313579/in/set-72157631868452754
Without:
https://www.flickr.com/photos/advance-design_parts_co/8129343557/in/set-72157631868452754