You can also use a iron pipe cap (2") as a hollow dolly and a shrinking hammer. Years ago I saw a tool a fellow from Vietnam had made. It looked like a flattened C or sideways U with a sharp end and a hollow end...hinged in the very center of the C. You could shrink metal like a champ as long as you could make the tool reach the damage. No matter what you did it would always hit the center of the hollow end.
