If you use a bat or anything else to get more room, be aware that you can tweak the fender in places that you will be surprised by. To get a little more room, you can trim the flange a little, or hammer and dolly gently, or use the bat, or cut the rear fender brace and pull out a little...then re-weld. If you are trying for more than maybe 3/8" of extra room, most of these methods have consequenses...you may see a larger door gap, buckles in the surface of the body, shorter distance in the wheel opening front to back, cracked paint or bondo etc.
John
www.ghiaspecialties.com