You shouldn't need it for a triangulated 4-link and coil overs. The angled upper control arms "locate" the rear. One of the advantages of the triangulated 4-link. If it's moving around too much I'd look into Johhny Joints or other rebuildable spherical type rod ends instead of the rubber RMS standard ends. True Hiem joints would be tough on the street for wear and noise.
A panhard or watts link is typically used in setups that do not self locate/center such as a 3-link, torque arm, parallel 4-link 4-bar, truck arm and sometimes for leaf spring applications. They also adjust the roll center height on these set-ups with the panhard by raising or lowering it. If you see a Nascar race and they are cranking in or out a few turns if the car is tight or loose in the pits, they are adjusting the panhard bar or track bar.
Wes
