These large, red urethane bushings and metal sleeves attach the aluminum rear end cover assembly to the frame. If your old bushings are bad, you will notice a looseness when you put the car in gear. These bushings will give a firm feel when engaging transmission.
Learn more from the following Mid America Motorworks Knowledge Library article:
Corvette and Why to Use Urethane / Polyurethane for Your Suspension
Prothane Motion Control