You really need to be sure the structural part of the car is sound before you start making big power. I mean the frame members, floor, brakes and suspension need to be able to support that big power. This doesn't necessarily mean you need a roll cage or even beefed up frame connectors but the basics have to be right. Get rid of any rusted metal in the unibody part of the car. The front fenders, hatch and hood and paint can wait.