Well, the 1st point to make is, to run a power steering system, you need a power steering pump!
On most landrovers they are engine driven from the belts. So he will need to sort that out.
Second one is to source a power steering box, and somewhere to fit it! Then source a suitable drop arm as the standard one wouldn't do it!
There was a kit that Chris Perfect used to sell, but he is no longer trading, there was also a kit fitted to one of the armoured landy's that were out in Northern Ireland but i've never heard of one for sale!
Its not a simple job.