what affect would it have on the spring if you cut the top and sides off the box they are stuck in? I would proably just make the thing twice as wide so the axle couldnt fall when your air born. move the bottoming stop a little to make room. All of the fancey off road suspensions run either triangulated 4 link or 4/3 link with panhard bar.
I had our W900 KW in for some waranty work and the had a fleet of new ready mix trucks. They use the sametheory BUT they have 4 links rather than three, the top two triangulated and rather than springs they have a fabricated beam with a huge rubber block. I say ditch the boaring beam and slap in four air bags. Add one more bag to each axle to lift, through in some lock outs and a remco. pick up the front or back one depending on what your doing, short wheel base or long.
Up here interstate 35W is as smooth of a road as you get and at 75 MPh them springs jump arond like jack rabits
Ahh.. sway bars, i have been thinkin about those as well, I was thinkin about using lock out hubs on one side for a disconect. You can buy blank torsion springs in various length/splines