The only potential issue in the front is that around the time when the disco came out they changed the claiper bolts from SAE to metric. If your bolts are SAE, then you will need to ream out the holes on the caliper and us the Disco/metric bolts.
In the rear you are dealing with the rotoflex...
What do you mean stuck? Diff lock or high/low? If high/low its most likely the solenoid. Pull it and seal it back up. If diff lock, the it might be the switch, look in the manual on the adjustment procedure.