I have been searching for one for some time and I have found that Engineered Performance will build one. Jeff said that he would like to build more than one, so, if anyone would like to have a limited slip diff for their 78 to 85 Riviera, Eldorodo , Seville or Toronado give them a call at 404-394-5776 or email them at tech@engineered.net. And tell them Ray sent you.