The Warbird Tech Series F-104 book I have by Jim Upton says that F-104A 56-0790 was modified with a U-2 nose for radar tests. There is also a photo of that airplane, and its nose section looks uncannily the same as this Norwegian airplane.
First of all, I think everyone would agree that Norewgian 890 did not fly in this condition during its operational career. I think if it did, there certainly would have been photographs taken of it, and some interest would have been paid to them long ago.
But, looking at this airplane, and knowing that the basic airframe was essentially a U-2, you can see that whatever this nose may be from, it seems to fit perfectly. (It might be better to see without all the snow, however). I agree it may be possible that this airplane was used for special radar tests similar to those performed with USAF
56-0790. Knowing that the Norwegian airplane was used for battle damage testing at the end of its career, it is possible that its original nose was either missing or destroyed, and a new one needed to be fabricated in order for it to be placed on display.
I have trouble believing that a U-2 nose would by lying in a Norwegian warehouse, so there must be another explanation....
My head is spinning, I wish there were more questions asked like this one.