I've asked that question too
http://expeditionportal.com/forum/showthread.php?t=26596
I agree with the above,but would like to add:
1. M101 CDN has box and frame all in one, not to say it's a unibody.
2. The box is much stronger than a 416 trailer as it is reinforced at corners and midsection.
3. If I do move the existing tongue to the front of the "Subframe", I would reinforce overlap area under the trailer between the Subframe and the tongue with some C-channel. The C-channel would extend to the side Subframe of the trailer.
4. And you have to clean off the undercoating on the trailer before welding as it is likely to catch fire.