No need to worry about cracking your oil pan when you try bending it back, it is easily weldable. The best way to hammer them back I found was to use a hammer handle on the inside of the dent with the outside of the pan resting on a sturdy piece of wood such as a 2x6. If it cracks? Just continue to form the metal how you need it and take it to a local automotive or exhaust shop and they'll likely weld it up for you for a decent price, then just grind it down with an angle grinder or on a bench grinder, paint, and wolah. Good part about welding is you'll never have to worry about that area cracking again, haha.