um... have to disagree.
If the 90 is a Turbo Diesel or a 200tdi then just put the transfer box on the original mounts in the 90 and hey presto. Better still, use the transfer box from the 90 on the back of the auto box to keep the gearing about right.
Tunnel, seat box, bulkhead... no changes to any of them.
You'll need to ditch the viscous fan and fit an electric, you'll need to fit some new engine mounts and you'll need to mount the shifter somewhere, but otherwise it's a pretty straightforward task.