MK1 hubs are totally different, 3 upgrade paths for you:
1. Fit old square Audi 80 calipers & calipers
2. Fit adaptor brackets, TSR used to sell them they come up often on ebay
3. Fit Vauxhaull calipers, you need vaux calipers, pads & brake lines, and VW discs.
If you go the vaux route the problem is the bolt holes on them are larger than MK1 bolts, so you either need to fit a slieve into the caliper hole and find longer bolts, or find some shoulder bolts which have the right diameter to fit in the hole and have a smaller thread on the end.