As I understand it. For stock and prerun there is no difference. The change is regarding the Full Mod. It is now fully modified directly from the factory and should be a real beauty that is for sure. All prerun work is done by our man Chad. Once you buy an engine that is pre broke in for you, you will never want to own anything else. Plus for the cost over the stocker when you think about time and fuel.....No Brainer.