Can someone explain what the differences are between a TJ and a TJ2?

Mine has a build date of 12/2002.

Most importantly, will a centre clock unit from a KJ2 fit into my dash?

Then yours is Series 2. Mine is a TJ2 and has a build on 02/03

Anything BUILT after june/july 2002 should be a series 2.
There were some pretty big differences from memory, ABS standard, tiptronic, digital odometer, I think they may have dropped the 3.0L as an option too.

Thanks guys :)

Anything BUILT after june/july 2002 should be a series 2.

According to the service manual, there were updates effective from August 2001 and again in March 2002 (and an awd specific update in December 2002).

So, as i understand it...

Series 1 = up to 31st July 2001
Series 1.5 = 1st August 2001 - end February 2002
Series 2 = 1st March 2002 - end of production

Mine has a compliance plate dated August 2001. So it is a series 1 update. I think this update simply made the ABS standard on the executive, but that's about all. (I think - somebody correct me if I am wrong)