Here are a few pictures of the heater I pulled out of my '51 3100. It does not look like any heaters I have seen from a 1951 truck. I would like to find out brand/model it is so I can get an emblem for the front.
http://www.flickr.com/photos/75986785@N02/6825164411/in/photostream/ http://www.flickr.com/photos/75986785@N02/6825138801/in/photostream/ http://www.flickr.com/photos/75986785@N02/6825162713/in/photostream/
http://www.flickr.com/photos/75986785@N02/6825165867/