You're looking at custom work to fit a pickup bed on a chassis cab. The frame rails are straighter, higher and longer than a pickup frame. It's been done before, but it may blow your budget.
I know my Mammoth is 4712 lbs dry from Host based on my option choice. My rear axle weight is 5000+ lbs on my empty truck. Do the math on what your Mammoth will weigh dry with desired options then add your truck's empty rear weight, 60 gallons of water, your gear and tongue weight from a trailer you may tow. You will most likely be over Ram's RAWR and close to AAM's maximum axle rating. For me, there was no way I was going to purchase a new truck knowing I would start off over published ratings - I know my load will creep up in weight as we get used to the new rig and find additional things we want to bring along.
I may have additional weights tonight if the highway truck scales are closed and the scales are working.