It is best to buy the Chevrolet Performance kit from your dealer. It includes all the components needed including the speedo cal, and best of all when it is installed by the dealership it preserves your factory warranty.
I had the 3.91 kit installed in my personal Camaro and I love the results! You will definitely feel the difference.
Get more info below for the 3.91 kit as well as other cool stuff for your Camaro. And the best part is these components were designed, engineered and validated by the same team that developed your Camaro so you know they're the best. And when installed by your dealer many of these components are backed by Chevrolet and preserve your factory warranty.
http://www.chevrolet.com/performance/camaro-parts.html