I don't know how the original plating was done, either on heads or cylinders. I would think it would be easy to mask out newly plated tops for abrasive cleaning of any stray plating on the gasket and combustion side.

But I had newly cast 45 inch jugs nickel plated by International Chromium Plating in Providence Rhode Island due to their reputation for having plated a lot of motorcycle cylinders. They said the cylinders would be abrasive blast and plated - that's all - no mention of how areas would be masked and protected. I left it to them to do what they know how to do.

They were returned nicely plated with the bores clearly protected. However, I had some post machining done on the bores. The machinist was pissed because there was a little bit of nickel in a bore he did not see, nor did I, and it clogged his cutting tool. He advised to always get all the final bore work done before plating as it not possible to fully protect the bores. 

Anyhow, I notice a lot of 101's in Europe have black painted cylinders and heads (post original) and I have come to like the look better than nickel. I eventually acquired a 101 that spent its life in Europe and along the way the cylinders and heads were pained black and I really prefer that look to my plated 101 - obviously originality is not that important to me. But black painted heads on plated cylinders I think would not look nice.