I'm confused.
Basically a round-up, the mk2 has a shorter track of 42mm on the rear than front (so 21mm each side).
So people put on 15-20mm (each side) to even the rear out with the front.
It shouldn't make any difference if you have drums or disks, as long as you get the correct hubcentric (so has the ring coming off the spacer, to keep wheel central).
Also there are 2 types of spacers.
1) Bolt-on (where you bolt the spacer to the hub of car, then wheel to that spacer)
2) slip on (where you get longer bolts, and just sandwich the spacer between the wheel and hub)
Bolt ons can sometimes "cross thread" the bolt holes on the spacer, but then sometimes people do not like the longer bolts (also bolt on will be minimum of 20mm, and Slip on will be 15mm).
EDIT: misread it, Bearings are in the rear disc, need pressing out and in.