I very much doubt it.
It'll be interesting to see if a lot of EL cars all start coming with aftermarket speedos.
That being said, the auction sheet is not of the importers doing, as far as I am aware, so is accurate I suppose. Of course him telling you the Nismo guages have been there since new is him either making shit up or just passing on what he's been told. There's no way he could ever know unless he's known the car since it was knew, so that's a piece of bullshit right there.
The car looks absolutely mint so I reckon you may have hit a good one. The paint looks perfect, underbonnet is bloody clean and the steering wheel and gear knob look good.
EDIT: I missed the water pump change. That rings a massive WTF bell right there. 51,000ks and needed a new water pump? That's nonsensical.