Are you going with a 6 volt car? Kinda cool if you are!
The '66 VW's were 6 volt, I suspect that you're gonna need a 12 volt assembly. 67's were the first year, but they're a little difficult to find, maybe grab up a nice early 70's assembly with two speeds, that would work out well.
If you're going for a little more authenticity, and want to use the early style wiper arms, you can swap the '66 wiper pivots onto any later 12 volt frame.