IMO it is a legit US M3 blade. Below is another thread from a different forum. It does not have a lot of new info, but a number of pictures of additional Norwegian converted M3 knives. Norway converted M3 thread another forum

I live in the Houston area, and I have recently inherited a very large collection of WW2 German items and WW2 and present Soviet items. While I find these items extremely interesting, I am not a collector. I tried to post this in the For Sale section, but it will not allow me to do so. The items include Nazi flags, swords, Nazi marked firearms, medals and pins, a Japanese rising sun flag and Soviet medals, pins, badges, patches, daggers, flags and sword. I am interested in selling the entire collection so contact me if you are interested. Pictures available upon request.

Doesn’t look bad, a nice salty helmet.

The photos inside seem to be wire service photo originals. It's women's service topic. And the B-17 on the scrapbook cover has the sharkfin tail of the early models.

https://www.ebay.com/itm/306360264945

Do you have any photos of him or info that you can post?

Can antone help with an I.D. for this design. Mickey Mouse was not a big choice for use by combat units during  WWII, and I'm not certain if this was anything but a fantasy patch. Any help will be appreciated.

Here's the label from a 13th Division wool service coat from the same contractor.  

Here's  the pictures cleaned up. Not very pretty.

Two US Personnel pose with a German grave surrounded by wreckage in the Liri Valley NorthWest of Esperia Italy - May 1944 LIFE Magazine Archives - Carl Mydans Photographer WWP-PD   13th FA Brigade marked helmet