You will need a new harness. I believe that part number includes the harness. If not, there is a kit that includes the harness. Get a good set of AFR 165 heads, and a decent cam. Couple that with a good Cobra/tfs/Edelbrock intake and good exhaust will get you the 300 + mark. lots of 302 (5.0) info on the mustang website
www.corral.net