Sorry to lose track of this subject, I have been a little preoccupied the last few weeks.
The occupation carbines are uncommon here, your rifle has been heavily modified post Nazi modification. The markings give it slightly extra value.
The forend has been cut back, it should have a hand guard around the rear sight and as you suspected the rear sight has been "jerry rigged".
Norwegian rear sights turn up occasionally on the auction sites. "Correct" wood is likely nonexistent, but some "creative wood working" on your part could make it look close. Hand guard and bands are going to be nearly as hard to find, so any restoration would extremely difficult and expensive, likely much more than the rifle would be worth. I would have the head space checked and the shoot it!! I would only use basic ammo, no high performance or "+p" type. I have been shooting my Norwegians with standard loads for a number of years now with no ill effects. Have a gunsmith check it out and enjoy.