Well, the car is a unibody, so first you are going to have to support everything in the car so it doesn't move around when you start cutting..... Best suggestion I could make is seek the assistance of someone in your area who is competent and experienced in doing a back half..... Even if you have to pay him for some assistance and advice it would probably be the best money you could invest in the project.... One of the best books on Chassis Construction IMO is "Doorslammers", get a copy of it. Art Morrison has some good pictures and tech articles on their website.