Hello, I will do my best to work with you to answer your Volkswagen Questions.
Setting a cam on a VW is no different than setting up a cam on any engine. You need to use the cam manufacturer spec card for the particular cam you purchased. If you dont have a card or spec sheet. Set it at 0, no advance or retard. Retarding or advancing usually change at what RPM range the power is made. With a low RPM VW boxer it enjoys the lower RPM grunt in my opinion. Unless you are using an aftermarket aluminum case, with a counter weighted crank, RPMs over 5K will seriously damage the soft VW case.