There are bristle brush type hones made for nikasil that will most definitely clean up marks like that and are safe to use. My old 04 gassy had over 20,000km on the plating and was still within spec. The key in my opinion is to not try and get 100 hours out of pistons. I do mine at 50-60 hours max and have never had any seizures. See if this link works.
http://www.enginehones.com/niapho.html