A Nitro Special is still a Nitro Special. After market customized guns are nice, some better than others but not factory. The metal fit on a Nitro Special is decent but not very great. If that was a custom order gun Ithaca would either have used a Flues or NID as a platform. The wood would have been a much nicer grade of blank. That just looks like they took a field stock and carved it.
To me it looks a lot like one of the upgraded guns GIs had done in Japan. I knew of a Winchester 101 which had been restocked and engraved to look like a Kreighoff Crown Grade. The pattern was there but the fine detail was not. But the owner can choose to believe whatever he wants to but saying it does not make it so and when others, with far more Lefever or Ithaca experience don't agree with his views I put more faith in them than him.