One place the Washington's Ax problem comes into play, other than the body and frame, is in the large-piece panels that make up the roof, sides and other coverings of the car's insides. Since you're repairing and rebuilding your machine in order to be looked at, it can be easy to overlook the quality of these panels as long as they're unwarped and can be painted in a pleasing way.
But often, especially in very old models, it can be difficult to find panels that haven't been nearly rusted through. Repairing these damaged parts can be tricky, and most of us have neither the skills nor the inclination for doing the large-scale metalwork necessary to repair them. Even tracking down better versions and having them shipped can become difficult and costly, thanks to their size and scarcity. Remember that back doors, hoods, sides and roofs are all exposed to the elements for decades, and finding the perfect piece could verge on impossibility.
Keep your budget in mind, and, once you know you've searched enough to stick to it, give yourself the option of reevaluating your project. It's not giving up if you decide the expense and labor aren't going to be outweighed by the pleasure you'll get from completing the project: It's just smart.