Acid dipping will completely remove all rust. It is essential that the dip be followed with a very thorough flush, then phosphate or e-coat or powdercoat depending on your needs.
Removal of the subframe and complete disassembly will be required, and this is the perfect opportunity to restore the body mount pads on the subframe, as well as replace the mount insulators.
Vikki 1969 Goldenrod Yellow / black 400 convertible numbers matching