usually the new bolts for the rubber bushings have the round ends. I do not know of a source for the square end bolts. you may have to change the entire assembly including the end plates. Many suppliers have the assemblies including the bushings bolts and end plates, the bolts are welded to one of the end plates and bolt to the other, the rubber bushings are hand fit into the holes and the bolts will slide into them. You could also change to the original type shackle, it will require a lot of extra work.