Cap off the vaccum lines because you won't need them with the new axle but you will need them to make your part time light come on. It works off a switch the lines run to on the firewall. The WJ axle isn't a bolt in and would require new wheels as well since it has a different bolt pattern.

 

you would also have to run 16" rims to clear the calipers.

 

You could also pop your shafts out and remove the vacume port, cap it, pull the diff and install a inner seal form a non disco D30 and run the 2000 shafts (bigger joints) and have best of both worlds for the cost of fluids, seals and a couple hours works... (if the shafts/axle is free, you wont have to reset the diff eaither)

I would repalced the u-joints while its out if you do have te shafts out, jus tto save you a headache later.