If natural steel you can soak them in Evaporust (use a length of PVC pipe as small as they will fit into, cap both ends, fill with Evaporust, soak a couple days to remove all the rust). Once the rust is gone remove them and rinse them with laquer thinner (not water). After dry add back any inspection paint daubs you find then coat each one with RPM (ECS sells it) and reassemble them...You'll be good to go!

Most spring sets that were painted black were painted as a completed assembly so it's easy, just derust/clean them then bomb them with a dull gloss epoxy paint. Adding it until it's almost dripping off will give you a factory look, most look as though they were actually dipped in paint at the factory.