we need to know how much the rear suspension has been modified. it is common pratice to at a tri link which is a traction control device that attaches to the top center of the diff and runs forward to the body or frame and a panhard rod replacing the stock watts link. if the car has these the upper link bushings have to be removed usually replaced with foam rubber. if you do not have a tri link yeas you need bushings in the upper links.
dick