As there are few replacement panels for a 67 Cougar, the rust on the Dutchman Panel (between trunk and back glass) will have to be cut out and new pieces fabricated. It'll be time consuming for sure. In order to be sure any remaing surface rust is made inert, I maximized the effect of the Phosphoric Acid solution by sealing it under Saran-wrap.
Front End Removal:
Hidden damage on inner apron.
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