If you've got ANY movement in the propshaft U/Js then change them. Sometimes the full extent of the movement isn't clear until you remove the propshaft from the vehicle.
If these are OK and you think it could be the rear diff bearing then have a word with
Ashcrofts or have a look in the For Sale section to see if anyone has a spare diff. The good thing is that your diff is fitted to 90's, Range Rovers and 200 series Discos. It's a 3.54:1 ratio and I think yours will be the 10 spline type so there are plenty around.
As for the "clunk" from the transfer box, you can illiminate some of it by fitting a new, cross-drilled, output gear. They are £45 from
Ashcrofts and will take out some of the slack.
If the gearbox mainshaft is too worn then this won't make much difference and a new mainshaft & input gear is the only way round it. These can just round off and the first you know about it is when you loose drive!!
