Chuck, I'm no expert so bear with me. The quaife differential basically replaces the stock piece in the trans that has a history of grenading under loads like drag strip starts, extreme cornering, etc. It also transfers power from one wheel to the other to overcome only one tire spinning and allow more power to go to the ground.
For different options to upgrade the trans in this manner there aren't any real options. The least costly one is to install the "phantom grips" piece which basically imitates the action of the quaife by increasing pressuring on the side gears in your stock differential. However you must still remove the trans to install it and it does not aid in strengthening the actual differential to keep it from blowing into multiple pieces. That and it is only about $200 less than this price on the quaife.
If you're serious about the performance go with the quaife and have Terry do the install (if you can)!
HTH,
Rick
