Now that sounds like a good idea....
what do i need...
Dave will have a better idea, however AFAIK the 4 bold PAS box for the Discovery and Defender bolts straight onto the chassis where the manual steering box mounts and I believe the same shafts and pitman arm are used on both boxes.
The PAS pump is an Isuzu part superseded to IS-8970788790 (about $760 last time I was quoted - still need it)
Then there are the hoses from the PAS pump to PAS box and the one to the fluid reservior should be LR Aust parts.
The LR PAS reservoir and bracket. Should be the same on 90/110 and Defender 90/110/130.
Fitting the PAS pump to the engine means removing the cover on the timing case and slipping in the pump, no belts or pulleys, but will be some studs or bolts. Can look when I'm at home.
Diana