I own one too, minus the bayonet. I inherited it from my dad. I have shown it to many knowledgeable people and not one thought it worth putting in a museum. It was made by Mauser, something I believe the article failed to mention. Mine has the chrysanthemum intact. Years ago I managed to track down some 7.7 Jap cartridges and got to fire it. It’s a beast; that steel butt plate is very unforgiving.
An Arisaka type 99 made in Germany? That doesn’t sound possible to me. I’m certainly no expert. I’ve used this page for identifying different Japanese rifle markings.
http://www.radix.net/~bbrown/japanese_markings.html
Was your father part of the Japan occupation forces? Do you know where he was at? If the chrysanthemum is intact then it could have a far different story to tell than the one I have.
Regarding the Fort McArthur Military Museum. It’s not a huge place, and they considered what I have to be a very good example of the rifle. Other than the time it spent in their display case, it has been well preserved under a bed.