Well I dunno much about the spring under thing... how are the stock springs mounted? If they are also under the axle then it should just be a matter of moving the front leaf hangers and messing with shackles a bit but then again I dont know where that would put your ride height. I do know that prerunner type trucks try to add weight to the rear of the bed with a spare tire mount and fuel cell to help the springs work a little better and soften the ride.
-G
