Here is what a lot of the Jeep Cherokee guys do. Take the main leaf off of the extra set and cut the eyelets off of it, this will make it a couple of inches shorter than the main leaf that is on it now. Be sure to grind the ends nice and smooth so that they will slide easily. Take your leaf packs apart and insert the extra leaf under your main leaf. Leaf spring clamps can be purchased at most local auto parts stores along with new u bolts. If you already have the extra springs, it won't cost more than $20-$30 to try it.