This was a GM accessory heater (common to trucks), beginning in the late 40's (could even be a bit earlier) and continuing through late 1947/48 as the stocks were consumed. This same heater just used a name plate, color change for GMC trucks. It makes a last appearance in the Salesman Data Book in 1947/48.
https://www.flickr.com/photos/advance-design_parts_co/30615339350/in/album-72157631872034068/
https://www.flickr.com/photos/advance-design_parts_co/15672778350/in/album-72157631868452754/
This heater was available with/or without the defroster unit, that unit was also available separately through dealers. I went through my 1939, 41, 42, 46 Salesman Data Books (not mentioned or shown) I then went to my 1941 and 1942 Silver Books (great accessory sections) and the units shown (both Deluxe and Super Deluxe configurations) are like this.
https://www.flickr.com/photos/advance-design_parts_co/8129307001/in/album-72157631868452754/
Just for fun I checked the 1948 Silver Book and it appears there (no publication date).
https://www.flickr.com/photos/advance-design_parts_co/30615096540/in/album-72157631872034068/

1950 Chevrolet 3/4-Ton 3600
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