Another update:
The VANOS units are aluminum. I will be using steel bolts as originally planned. For a while, I thought they may have been magnesium (because the N52 block was magnesium). If that was the case, I was scared to use steel bolts because of the increase in stress during temperature changes and the likelihood of corrosion.
Since it's aluminum, I will use steel bolts. (Even though alu and mg are pretty close in terms of thermal expansion I believe). Im sure aluminum bolts would be better in terms of thermal stability but I just don't trust their shear strength.
Aluminum seems to be more resistant to corrosion with dissimilar metals. I will probably use a Zinc coated steel bolt.
These look promising:
http://www.mcmaster.com/#90327a138/=qwmk0y