D Dart package ?

In 1966 I asked the service manager at Chuck Hutton Dodge in Columbus, GA about changing out my 7.25 open diff for an 8.75 limited slip. I agreed to pay for the 8.75 if my warranty would be valid. He called me in when the district factory service rep was in town and I brought my '65 Dart GT in to speak to him. I had gone through 2 spider gears at Chrysler's expense under warranty. The factory rep told the service manager and me that changing the diff would void my warranty. True story!