I'd be VERY reluctant to try pulling loads like that with anything other than a new, purpose-built truck with a LOT of factory engineering in its pedigree. You're getting into at least medium-duty Diesel territory with loads like that, and stopping and steering a rig like that with some sort of home-brewed suspension system could get deadly dangerous not only to you, but everybody who shares the road with you. A commercial vehicle enforcement officer would probably get writer's cramp in his ticket-writing hand if you ever got stopped and inspected.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!