Another thing to consider is possibly the hole in the rear sight was for a jig made specifically for converting these to a sporter.
Its hard to say, but since the barrel length doesn't match up with any known examples and this is clearly sporterized, I wouldn't be willing to trust this example for any information on Norwegian Krags as a whole, unless you had a specific known pattern to compare to (maybe yours and Nabs were sporterized by the same factory).
yes - that possibility is definitely there, though I would expect a factory sport job would still retain the middle barrel band. This is clearly a home job on the stock.