You can have a Recirculating heater or and aftermarket brand, there were several brands, Arvin, B.F. Goodrich, Montgomery Ward, etc. Here are a couple pictures to help with your I.D.
http://www.flickr.com/photos/advance-design_parts_co/8377841188/in/photostream
http://www.flickr.com/photos/advance-design_parts_co/8258511484/in/set-72157632208362076
The recirculating heater has no Ranco and a plate covers the firewall opening.
http://www.flickr.com/photos/advance-design_parts_co/8129058609/in/set-72157631867396207
http://www.flickr.com/photos/advance-design_parts_co/8129332680/in/set-72157631868452754
This is a 1947 vintage square heater design, most aftermarket types are of similar construction. The switch you speak of (again there is a wide variety) is how these heaters were controlled.
http://www.flickr.com/photos/advance-design_parts_co/8129352382/in/set-72157631868452754
Hope that helps, if you can get a picture I can help identify what you have.

1950 Chevrolet 3/4-Ton 3600
More pictures on Flickr