Can anyone here identify this radiator? Maybe out of a 3/4 ton or bigger truck?

http://lymanhall.smugmug.com/Other/Chevrolets/i-q7CG87W/0/L/Radiator-1-L.jpg

I'm curious about the purpose of fitting on the radiator tank, and the reason for the top petcock.


1953 Chevrolet 3104 1/2-Ton
In the Stovebolt Gallery
More pix