If you already have a cone unit and you search out a clutch unit for a street car, you're wasting your money, IMO. The cone units CAN be refurbished. I've done several. As long as everything looks good, all you have to do is chuck the cones up in a brake lathe and remove about .100" from the small end. When they wear, the small ends of the cones come in contact with the outsides of the case and they no longer grip the case. If you remove material from the small ends, this restores the grip that was lost. You need to add an equal amount of shims between the side gears and the cones, though. Although this repair is not covered in any book, it works well and will not cause any problems as long as the rest of the unit is in good shape.
