I THINK...but do not know...that the stock military 6.2 motors came in black. I have only seen one motor that was green...it belongs to my brother-in-law...and it was a gov't rebuilt from Toelle. So, based upon my very small sample size (seven M1009s and one M1008 that I've personally owned and one M1009 that my brother-in-law owns), I think that the green motors were rebuilds. However, I see that someone just posted that he is buying a truck with a rebuilt motor that is black so, perhaps, there is no hard and fast rule.
Bruce
Olney, MD
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1991 M149A2
1989 M932A2
1989 M925A2
1989 M101A2
1988 M977
1988 M105A2
1987 M1045
1987 M105A2
1985 M1009 (3)
1970 M149A2
1964 M129C
1963 M332 (3)