The M series of that vintage were painted a 3 color cam. The colors were flat black, olive green, and flat green. On the cam scheme shown below, 1 is olive, 2 is black, and 3 is green.
Here is a side view of my jeep showing the cam pattern.
I have the patterns at home for the M series vehicles, including the trailers. Unfortunately I am wintering in warmer climates right now, but should be back home in January in case nobody else details the patterns.
I recently noticed that Aaardvark surplus in Ontario has original 3 color cdn cam paint in the gallons. It is likely getting pretty stale by now, but with enough mixing, could be made to work. There are some colors available from the US that will also come close. For the flat black I just use the tremclad flat black.