Shaping metal is not how hard you hit it, it is where you hit it. Although this book was written almost 60 years ago, it is still very much on point. http://www.amazon.com/Key-To-Metal-...automotive&qid=1295126182&sr=1-1 And of course you must remember you are working with a vehicle that was produced around the time of the writing. It also deals with metal shrinking. I would suggest reading the book before you do more damage.