If I were considering it, I would tell myself the work involved was not worth the dividend from past experience. You will need access to your own welder, etc. and the ability to handle heavy parts. You would be ahead to have your own machine shop to make the needed adapters, etc., or it will be cost prohibitive. You will still end up with a greatly underpowered truck if you intend to use it for any kind of hauling work.
I put a Hendrickson tandem out of a civilian gas powered truck under one of my M135's to get the power divider so I was not running locked rear axles when hauling heavy loads on the roads, but could lock them off-road. The ratio was slightly different from the front axle, so I designed and machined up a dog clutch for the front axle drive shaft so I could manually shift it in and out when needed from the cab.
I did not know the fellow, but a guy bought the axles out of an M35 at the local scrap yard to put them under his M135. He returned the axles a month or so later having given up on it. I do not know the details of his experience, only that he ended up not doing it.
If I had known then what I know now about how much better the M35's with the multifuel turned up are for power, etc. over the GMC I would never have done it. I was young and ambitious then!!
Regards Marti