Personally, I would use a compound called Duralac, which is both a locking type compound but also one that prevents dissimilar metal corrosion. Used a great deal in the aircraft industry and also in sailing where there is often a corrosion problem between s/s steel bolts and aluminium castings in a salty environment.
Works brilliantly on my boat - unfortunately, thats where it was when I put my own bars on.
Dont forget to torque the bolts correctly. Those castings are fairly delicate.