I restored the front springs on my '67 by soaking them for about a month in big Rubbermaid tub filled with old, used, oily Evaporust. After that, I washed them with soap and water, wiped them down with acetone, and then applied Testors gold and yellow model paints to replicate the stripes (I have since found that Americana brand acrylic paints sold at Michael's craft stores work much better for replicating paint markings - and they are lot less expensive as well).
Finally, I warmed up the springs in our kitchen oven and applied a liberal coating of RPM (Rust Prevention Magic) that is sold by NPD and other Mustang parts suppliers...
So far the only issue encountered was during the re-installation of the springs. RPM leaves a slightly waxy finish on the parts, and the spring compressor kept slipping - but it's been about a year since I treated them, and there's no rust on the springs. It will be interesting to see how well the RPM holds up over the long run...