As discussed above, two heaters in 1951 were available. The decals replaced the aluminum plate after 1950.
https://www.flickr.com/photos/advance-design_parts_co/8129448404/in/album-72157631868452754/
Recirculating hardware.
https://www.flickr.com/photos/advance-design_parts_co/8129444438/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8129418793/in/album-72157631868452754/
No heater or recirculating heaters came with these plates, if the inner plate is in place I would lean toward that or the after-market as being installed at some point. If Air-Flow those plates would be long gone.
https://www.flickr.com/photos/advance-design_parts_co/15838946822/in/album-72157631868452754/
The Air-Flow heater with Ranco had considerably more plumbing/hardware as shown.
https://www.flickr.com/photos/advance-design_parts_co/44267047400/in/album-72157631868452754/
https://www.flickr.com/photos/advance-design_parts_co/8130478168/in/album-72157631870734114/
The after-market brand is an Atlas, one of many brands and styles and period correct.
https://www.flickr.com/photos/advance-design_parts_co/38538349410/in/album-72157631868452754/