Did you get it from this guy?
JAPANESE whetstone 70+old NAKAYAMA plane sword razor - eBay (item 200359676682 end time Jul-07-09 15:33:03 PDT)
I asked him a question but he never replied. The characters do not look like the ones on the more traditional Nakayamas. They are comparatively cheap so I would really like to know what you think of it.