If ride, mileage, etc. are most important to you, consider leaving the Jeep alone. Lifting the Jeep will certainly lower your mileage (especially with 35s) and will most likely negatively affect the ride. Handling will definitely be worse. I believe you would have to lift the Wagoneer about 6 inches to fit those tires. Anything including and over 4 inches will require replacement of some steering and brake components in addition to springs. My Wagoneer is stock as well, but I would like to raise it 3 or 4 inches for off-roading. The FSJs have excellent clearance from the factory and are very capable as equipped. I will probably install 31 or 32 inch (x 10.5 inches wide) tires on the factory rims. This way they will still fit in the wheel wells without trimming fenders. Good luck on your project!
1990 Grand Wagoneer