Does it have 9 inch differential ?

For starters, you have an 8.8 inch, not a 9 inch. Limited slip, or in Ford-speak, "Traction Lok", was an option that could be found under 3 different circumstances on the 92 Lincoln Town Car. First, it could be ordered as a stand alone option. Second it was included in the Trailer Tow III Package. Third, it was included in the Performance Handling Package. On the driver's door, there is ain information decal. On it will be an axle code. Generally a number means open differential, a letter means a Traction Lok, and the particular letter or number denotes which axle ratio you have.