Why so much lift?? For off-road use the center of gravity should be as low as possible. Just barely enough lift for fender clearance of whatever size tires you want to use is all the lift that should be used.
Also, even though the current owner had no choice, an E450 chassis instead of an E350 chassis is more preferrable for several off-road reasons. We love the rock solid handling and stability of the E450 over-kill chassis under our small 24 foot motorhome - which we do take carefully off-road on occasion.