I would guess the UDI are having some confusion or translation errors. The actual form seems to indicate only that you need to complete it, in triplicate with photographs, and submit it. That the Norwegian mission will then forward two copies to the harbor police on their own, and that pending permission from those police, they'll approve and return your form.
Two months before leaving your home port would of course be impossible for craft which are not arriving directly FROM their home port, I can't help think that even the Norwegians are more logical and practical than this and would not expect it to be an issue. I think you'd just fill out the triplicate form, make sure they have two months to process it and mail something back to you, and then go.
But to be sure, why not call (or visit) a Norwegian Consulate? Or even a US Consulate and ask them to pick up the phone and do something diplomatic...like call a Norwegian counterpart?
If all else fails, just go. Announce on your arrival that you have come Viking (that's a verb) and if they'll just pile up all the women, gold, and cattle at the dock, you'll skip the burning and pillaging part and they can keep their crops. Hey, it puts thing in context, they should be used to that by now.