The source of that information on using a radiused throwout on diaphragm clutches was the owner of Tilton Clutches in Buelton CA. As I understand it, it applies to straight-finger diaphragm clutches such as GM sells, not bent-finger units like Centerforce The radiused-face throwout keeps the clutch action from being "notchy" as the angle between the throwout face & fingers changes during a disengagement stroke. Many Corvette people don't even notice this, so....