OK, I am posting something usefull for once. This will tell you all the bits you need to convert a 90spec Mk2 from non PAS to PAS.
PAS Rack (with tie rods is easier).
PAS Pump and belt.
PAS Pump Reservoir and mounting bracket plus bolts.
All the piping
The shaft from the PAS rack with the two UJs on it to connect to the column. (you need this as the non PAS and PAS spline sizes on the rack are different)
The longer bolts to mount the PAS Pump via the Water Pump.
I think that's it!
Edit : According to the main man RJ, the rubber boots on the shaft linking the rack to the column are also different on a PAS car, so you will need those too.

Some new PAS fluid!