The M101 is a good platform. It really isnt TOO heavy. I do have several M105's here (2700-3000 lbs empty). I use them on my farm for various things. I usually have one with 3 ton of small gravel instead of salt for my 3/4 mile long drive. I have also had the pioneers trailers, nice. I really like the M105 for the increased space, 6x9 instead of 5x8, I also have just "stolen" the bed, bows, and tarp to marry to my own custom lowered dumping frame. I did just pick up an M105A3 which has 22.5" tires and a surge brake (the first version with that option). I may steal the bed off of it for a "modular" system for my F-350 diesel dually crew cab or F-550 gasser. I want to have a flatbed (with Autocrane), army tarped bed ,and a Gitchner Shelter for the back. I can transfer them via forklift. Each truck has/ will have custom attachment system.
Good luck, with your build Jronwood