Back off the pinch bolt in the shock arm a long way and you can spring the arms apart a bit and then drive a large straight bladed screw driver in as a wedge to keep the arms separated a bit and then set the arm over the bushings and insert the bolt. Pull out the screwdriver and tighten the bolts. You should have a 2" spacer under the shock arm before tightening the bolts. Actually, for the poly bushes you don't need to have a spacer in place first but if you still have rubber ones in the lower a-arms, you should still use a spacer. And don't forget to lube the poly bushes or you may have a squeak.
Dave