Jeep Cherokee Forum - Transfer Box Help - Replaceing the Viscous Coupling

Hi All,:help:

Help and your thoughts needed, befor I go down the wrong route...
I have 1998 Grand Cherokee Ovis with a 4 liter stright 6 and its got 140K on the clock. It is my DD and stays on Tarmac only rarely going off road.
The Viscous Couple is on its way out in the transfer box.
My Choices seem to be:
Replace the vicouse coupling.
So is this easy to do ?
How do I go about this,is there a write up anywhere?
Or
Replace the transfer box with one that has 2WD and Part time 4WD and constent 4WD.
So can anyone tell me what transfer box is fitted to my car? What transfer box I need to lay my hands on to achive the new drives?
Thought wont a new transfer box have a viscous drive and that too will need replacing? How difficult is it to do the swap?

Basicall I need guidance and help deciding which route to go and how difficult that route might be.

Thanks in advance.
Markie in the UK