Im gonna put some leveling blocks under the back of my truck to get the rear leveled up with the front. I have 1ft of clearance from the top of the tire to the wheel well up front and 10.5 in the back. Measurments took from level ground. Is that the app. way to measure or do I need to go from the center of the caps? My question is if I get 1.5" blocks will i need longer U-bolts?