I fitted PAS on my 5 door 1.6 driver. Looked in Trade-it for a GTI stripping for parts.
All you need is pump, pulleys, belts, and the complete subframe.
It was a bugger to fit mine as the Driver steering universal coupling is different to GTI so i had to change that aswell.
Means i got the GTI anti-roll bar aswell!

Easy to change on a GTI, just drop subframe underneath, (four bolts i think) undo hubs, then underneath dash (by pedals) undo steering column, replace with PAS subframe, attach new column, fit pump and belts and from what i remember thats about it?!

May have missed out something important in there i expect?!