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There shouldn't be any differences. New model years were 1997 (X308) and 2003 (X350). NRMA lists an interesting feature of the 5 speed gearbox found in the MY97 XJR's- two reverse gears depending on normal or sport mode...a little strange.
1987 Jaguar Sovereign - Metallic Green
3.6L DOHC 24 Valve