Unless your doing extreme off roading, I wouldn't bother.. That said - if your doing extreme off road stuff, personally, I wouldn't be using a 2004 disco2, I'd be using a disco1! - TC and CDL should be more than sufficient for a standard discovery 2... Ours hasn't got CDL fitted, but the TC system has always kept it going in the direction its pointed, even with the road tyres that are one it!
Just my two penneth - in answer to your question, yes, you can fit them, but as thebiglad says - it'll be useless if you don't have CDL.
By the way - you can't have full locking diffs AND TC - TC doesn't detect wheelspin if all 4 wheels are at the same speed, just incase you didnt realise that!!