If you want to stay with the stock Super Beetle ball joint then look at the Porsche based brake kits at
http://www.vdubcustoms.com. They will take the Porsche 944 hub and machine it to fit the Super Beetle spindle. They will also machine the Super Beetle spindle to accept a braket to mount the 944 caliper. This will also solve the problem of positive camber that the 944 spindle will give you. It is fairly expensive but it solves two problems at once.
Randy