Even if you have big rust holes, like you could put foot through the floorboard, there are several companies that sell complete panels that can be welded onto your old body. Check out either Four Wheel Drive Hadware in Columbiana, OH, or Quadratec in West Chester, PA.

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.