Hi Bob
Here is an old thread on Chevy oil filter locations
http://www.mapleleafup.net/forums/sh...ght=oil+filter
As Peter points out the early location is horizontal in the frame rail on the intake and exhaust side of the engine which is the passenger side of the CMP. This location makes it a real pain to drain as the exhaust pipe is right where the oil pours out.
Now to add to the fun there is a service bulletin on relocating or replacing the filter up on the manifold. So you may find the higher location on Pat 11, 12 and fire wall location on for conventional cab Chevys. My 1941 Pat 12 C60L had the oil filter down in the horizontal frame location as did my 1942 Pat 13 C60S but my 1945 HUP has the manifold high filter location.
Cheers Phil