Does anybody know where the engine number is on the 98XJR I looked in the thermostat area can’t locate it

 

Near the front of the LEFT cylinder head next to the thermostat tower UNLESS the engine was replaced later on with a newer block.

The newer engines have the number on the left side of the cylinder block aft of the motor mount.

 

The pictures below show the engine number location on a 1999 XJR.