After boxing a small section of the frame in the rear, we pierced it and welded in tube similar to the shackle mount in the front. The shackle angle that you use will depend on the arch of the leaf spring. Our springs are pretty flat. To keep the shackles from bottoming out in either direction, we welded up the mounts so they leaned backward approximately 10 degrees with no weight on the suspension. This gives the spring plenty of room to grow in length as it compresses under the weight of the Jeep.