Never seen that oil pan. Was that a military thing?
Yes it is a military thing. My original 1940 Chevrolet part manual for these trucks differentiates common civilian parts (which there are many) from unique military parts. It lists the pan as an exclusive military part number and a new part for the 1941 model year. The crank case still takes just 5 quarts like any other similar engine, but this model has a much longer pickup tube to work with the deeper pan. I presume it was designed to prevent oil starvation when the vehicle was operated on steep slopes. Notice that the pan has a seam along the middle suggesting it used a civilian top portion with the deeper sump welded to the bottom.
