1972 Buick Riviera Boat-Tail 455 Parts or Restore needs rear frame & tin work

This car has been sitting for 21 years and now needs a frame and tin work. I have not turned the engine over. the ignition is taken out and it will not turn to the start position. I was told the interior was redone before it was parked and the engine was tuned. and new tires 21 years ago. the interior is in rather good condition.the doors close nice . the trunk is locked still . all the glass and lights are good and most of the chrome. the wheels are not to bad. the car does roll fine.I would rather sell this car as complete original instead of parting it out.That will be the next step. Thanks for looking