Do you mean a full frame and entirely new suspension? If so, IMO that would be a lot more work and expense then is required. The rear end is the weak link in the car, just buy a back half frame section and exten the rails to the box that forms the structure for the front suspension. Add a roll cage and some sheet metal for the floor and wheel tubs... Not knowing what your experiece level is, I would caution you that this is not a "1st timers" project and will require a lot of advanced fabrication and welding skills....