pencero said:http://umiperformance.com/catalog/index.php?main_page=product_info&cPath=8_60_72&products_id=83
This is an expensive part but it can help prevent the car from bottoming out for a long time. It's designed to help a lowrider never bottom out but once your car is on 24's similar principles apply about too much flex letting the tires rub and all that.
You don't need those. Should you decide to go up to 6s you will probably want to get UM I extended rear trailing arms. I bought them for my Cutlass when it was on 6s.