ask your shop if they just need the main arch(s). if so clamp them several inches away from the center bolt on each side of it & I would crack that nut with a nut cracker then remove the nut/bolt & undo the clamps evenly. that is a special bolt & the threads tend to get boogered up from road debris & if the nut is tight & you crack the bolt with using just a wrench then you'll have to search for a new one