[Model51]

Just for fun, did you know there are at least three different air compressors for Ford trucks? One is mounted on the side of the transmission for small jobs like inflating a tire, another on the front of the engine was used to provide compressed air for a pneumatic brake booster system and yet another is a PTO driven air compressor for higher air demands.
Ford of Canada provided the transmission mounted air compressor for many trucks built during WW2. The air compressor (Westinghouse, Bendix and others) used for pneumatic brake booster systems came with all the other brake control parts. The PTO drive version is aftermarket equipment and came in many shapes and sizes.