The original brakes that come with the Vanagon are not very good, especially on the Syncro Westy, there is a lot of weight. There are South African Vanagon brakes that you can install, they take vented rotors but the piston size is still the same as the later type Vanagons.
I installed a set of later Audi 5000 turbo rotors with the Girling double piston calipers that came of the same car. You have to machine the caliper bracket to match the holes of the steering knuckle and use 8 mm thick spacers with M16 or 5/8 " bolts for this.
In the rear I have calipers from a 2004 Jetta VR6 or Audi A4, they take vented rotors. I have used 1985 Audi 5000 Quattro front rotors, they are 280x22mm. The calipers are mounted, by using an adaptor, to the bearing housing.
The brake hoses are from a 2004 Passat AWD, they use a banjo type bolt to connect it to the calipers.
Also, the rear hubs have to be machined down so that they fit inside the rotors. I had to go to a bigger wheel and longer studs, using 17" Audi S6 mags.
I am using synthetic brake fluid so I had to clean out all brake and clutch lines, it does't mix with regular brake fluid.
Once the van is on the road, I will check out the brakes to determine if the rear brakes lock up too easy on a wet surface, I may have to install a different pressure reducing valve.