Norwegian Krag, number 351, was built in 1898 at Kongsberg Vapenfabrikk, as a Cavalry Carbine model 1895.

It likely was altered at a later time to the Mountain Artillery/Royal Engineers sling arrangement.

IMHO - It's only a wild guess as to when and how the bolt got switched.

Since the action, stock, and likely barrel numbers match, I doubt if the bolt switch was official.

(Norway was an 'occupied country' during WW2).