Like where the frame and rear cross member meet? I think they are about 3 inches inboard of the frame mount on each side i think. It has bolts on each side of where the frame and crossmember meet and i think those shackles are over the inboard set of bolts.
It uses seven 5/8" (16mm) 10.9 grade bolts on each side. 6 come through the cross member into the captured nuts welded inside the bumper and one on rach side coming up from the bottom