Sorry but the polarity of the electrical system causing a vehicle to rust theory has been debunked long ago. Any first year chemistry or physics student and some of the better high school students can understand how and why its just not a factor in the actual formation of rust on vehicles.
Given the complex bases and acids in common dirt and organic materials vehicles are exposed too its easily shown how environmental influences however do account for an oxidation or decomposition effect to occur on any metallic material. Its just basic chemistry in action.
Most likely what has happened is that your vehicles protective layers of paint and the more resilient outer shell of metallic oxides that form during the manufacturing processes has deteriorated and the more susceptible inner core of the metal is now exposed.
That tough outer skin has begun to break down after 60 years and the purer inner steel is exposed which corrodes and rusts far faster. Once it starts blistering it rapidly breaks up the surrounding skin and grows.
Thats why they call it cancer on vehicles. Once it starts it either has to be dealt with quickly and often with evasive efforts or it quickly takes over and destroys the very material its apart of.
This is a very common effect I see on antique machinery as well. After so many years the metal just starts to break down regardless of what polarity of electrical system is used. Even Machinery without any electrical systems has the same effects occurring in the same relative time periods. Its just natures way of reclaiming the materials.
If you would like I can put in a word with the local witch doctor and he can shake a magic stick in your general direction while doing a dance. That might prove itself to be just as useful as the reversing of the polarity of the electrical system will!
(or it could counter act it too.)