Babaganoosh, if you want to run the 315s (34"s), you will have to run at least a 2", if not 3" body lift if you don't want to trim your fenders. A zero rate will let you move the axle forward enough not to hit the inner fenders by the firewall, but then you will definately have to cut the front "fang" off the fender.
When my truck was stock height, I put on a new set of 35X12.50 BFG Mud Terrains (KM1) and I couldn't even turn the wheels without rubbing, so I trimmed the fenders. The tires still hit the metal hard when I was pulling into a driveway or something. So I installed a 4" spring lift (and removed the anti-sway bar). This kept the tires off the fenders until I went down to the off road park. The very first little ditch I drove through had the tires all up on the part of the fenders that I had cut out and actually cut chunks off my tires. More trimming was required. Soon a zero rate will be going in to move the axle forward 1.5"
My point is, if you want to run tires that big with a 4" lift, the only way you can do it without trimming the fenders is either installing a body lift or somehow mounting the springs lower, like making a spacer where the front of the springs mount to the frame. Only thing about that would be that it would change your castor angle. Not good. What about an anti-sway bar? If you could run a stock style sway bar and set your bumpstops right, I think you could do what you're wanting to do.
Stiff front springs might keep the tires away from the metal too, but it looks like you've already got the springs you're going to run.
ive gone soft! 
