[jimmo]

Ok, here are some photos to try to demonstrate. the first photo shows how deep the nut is recessed inside the VW pulley on my stock alternator.
The second shows the popular gm pulley on my stock alternator but the the 3rd shows how far it needed to be spaced and it rides on the threaded area of the shaft.

The 4th photo is the 11mm offset gm pulley positioned on stock alternator so the belt lines up. The 5th photo shows there are not too many threads left for the nut. Probably can use it if you lose the lockwasher but I wouldnt recommend that.