Overall length of my rig is 40' from bumper to bumper.
Not sure of what your asking with the 57% balance, but my wheel base is 28'. I have not weighed all 4 corners independently. My overall weight out of the factory was 28,550 with approx 200 gallons of fuel. I have had a number of motorhomes and will say that this setup has by far the best balanced feel of them all.
My water & sewer are not heated, I am sure you can get it.
If you order a new truck with tandem axels you'll have 4 air bags, I don't know that any of the class 8 have a front axel air option, but they might. I added aftermarket air bags to my front axel. (highly recommend)
Couldn't tell you what your overall length would be on either chasis, I have never measured them. Some things which may very your length; are we talking day cabs or sleepers, new or used, are you going to modify a sleeper cab.
I will tell you that I would do what ever I could to keep overal length at or under 40'. Anything over this and you start to really limit your access to campgrounds and many states for that matter. Also my wheel base is long and it takes a country mile to turn this thing, I have gotten very use to the size and determining turning points in tight places, but it definetly takes some pre planning and looking ahead. (Specially when you have a car behind with 4 wheels down)
2003 28' Show Hauler Motorhome on a 1995 FL 120
www.showhauler.com