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It was over on the Marion Valve Engine build thread, here:Started here, with link to the instructions I followed:https://www.instructables.com/id/High-Quality-and-safe-Nickel-Plating/http://www.modelenginemaker.com/index.php/topic,9312.msg210244.html#msg210244More a few posts after that one, and here toohttp://www.modelenginemaker.com/index.php/topic,9312.msg210244.html#msg210244Its quite easy to do, I recommend getting a variable power supply if possible so you can adjust the voltage - higher is quicker, but rougher finish, around 6 volts is good. The distance to the part changes it too, the closer the faster/rougher. Distilled water, non-iodized salt, a Nickel rod/plate for a source, and a plastic container are the only other parts you need. No nasty acids involved, and you can re-use the solution so a lidded container is handy to store it in. I've since done a bunchof knobs for the Lombards up at the museum, as well as parts for several models. After plating, you can buff the plating to shine it up.
Wipe down with an oily rag after running and drying will do unless you store the engine in adverse conditions. After all the inside is bare iron and won't be getting any additional coatings.Biggest problem I can see if plating the cylinder is keeping the bore free of plating.