I will say this only once you can put 1 ton axles under an M1009.
1 the best gear you will get in an 14t gm is 3.73 with D60 if you use an D70 rear you can get 3.54 in both config just rember the cummins does not turn as much rpm as GM 6.2L
and that will be your short fall.
2 you can install an cummins in Chevy or GMC with out cuting up the core support I done it many times there will half to be some frame mods to set in and have all of your angles in line so you dont have binding or bad vibration do to your angle or degree are off IE drive line and or center line of chassis.
3 AS for me if I was going to do this mod I would buy an first gen Dodge w250 just for drive line eng trans and t case or you can these trucks can be bought for as little 1200.00 to 2200.00 in running order 89 to 90 will have 3.07 gears front D61 d70u rear
or 91 to 93 had 3.54 gears.
4 So an conclusion It is your M1009 CUCV and you can install what your ever you want.
5 If you never install or rebuilt an 3.9 or 5.9 Cummins and installed them into other things
and just look at posting on the internet and or read mag.
6 Last but not least the only way you know it you had to been there and do it IE install.