Right, MK4's came in both ABD and NON, it was a optional extra.

The master cylinder you are best buying is the S2 NON ABS item. S2's have the biggest ones. With a NON ABS one u can simply get the brake lines off any NON ABS MK4 if you want to.

The compensators reduce the braking load to the back wheels for safety, ABS cars have "load aportioning" compensators, they are linked to suspension and vary depending on what the car is doing. NON ABD cars have fixed rate compensators under the bonnet