That depends on your requirements for a 4x4.
If you want a daily driver that can go up to Fraser, with good vision & has a tray, then I would suggest the later model power steering box.
If you want to start running some serious trails, rock crawling, of comps then definately the x-over steering.
You will need: Power steering box, power steering pump, resovoir (where is that spell checker

) High pressure line (pump to box), low pressure return, line from resovoir to pump, pump mounting bracket, if you have a/c then you will need a 3 belt pulley for the end of the crank or only 2 belt pulley if no a/c, belt, plus the resovoir mounting bracket.
You will need these components, weather you use x-over or not.
You can add: steering arms, IFS steering box instead of later model box, drag link, 4 x ball joints, pitman arm for steering box, plus the rod that goes from the pitman arm to the steering arm (I always forget its bloody name ), if you want to go to x-over.
Depending on who you speak to you MAY need a suspension lift & to remove to anti-wrap bar on the front diff.