That is the swaybar endlink. I'm sure there are several members here selling them in the for sale section or you can get aftermarket adjustable endlinks or I think I've also seen some people make their own with parts from hardware stores, I believe.
This question kind of threw me off from the rest of your questions but I would go with what the manual tells you as far as octane unless your boosting, then you would want to run higher octane.