Nickel plating on cast iron is very tricky. I do it in the lab for metallurgical mounts. If not done right it can easily flake off. Surface preparation is all important. You cannot grit blast the surface for preparation. Your best success would be to go with a schedule of copper strike/copper sulfamate plate/buff/soft nickel plate/hard nickel plate. But then it'd be silly to use the car afterwards.
Some outfits sell cadmium plated rotors. Search the archives using "cadmium" and "rotor".
95 E320 Cabriolet, 131K