Go get yourself a riveting tool with some 3/16th steel rivets at the hardware store. Start at one bottom with a pair of vice grips. Clamp the two pieces together, Pre-drill the hole, then add a rivet every .5" - 1" inch. Work your way around to the other end. Then add a shallow relief cut in between each rivet. Take a BFG and then GENTLY pound the relief cut pieces up into the wheel well. If done correctly, you'll save the unibody and add some clearance at the same time.
If there's not enough material for the rivet trick, you'll have to weld in some 1/4" or 3/8ths bar to fill the gap. not fun to bend.
Good luck,
Jim