Nice looking type 99 considering what its been through.
Dust cover is missing (expected) Everyone reports that the Japanese soldiers threw away the dust covers whenever they could. (they rattled).
No monopod, which is also common, and there were rifles that never had them.
Intact "mum", which is a big plus to the collector value, and is assumed the rifle was a battlefield pickup, rather than a gun surrendered at the end of the war.
The AA "wings" on the rear sight (used to establish lead on low flying aircraft), and the style of the bolt knob show its not a late war production version, nor is it the fabled "last ditch" rifle.
The 7.7x58mm (7.7mm Jap) is the ballistic twin of the .303 British. Same bullets same speeds, same pressures. the only difference is the case dimensions. Brass can be formed from .30-06 cases (GI .30-06 is what I've used) or sometimes you can find commercial cases, I bought a 100 from Graf's some years back, so I didn't have to make any more 06 into 7.7mm.
As will all the 99s I have seen, the stock is made of several pieces. There's probably a joint under the forend band. Be aware, sometimes the glue has become "one with the ages" and I've seen one come apart when shot.
(didn't break, just came apart)
Arisakas don't command the $ that some more desirable milsurps do. Your gun is in pretty good shape, for a combat veteran, and the intact chrysanthemum marking means it should be near the top of the price range for rifles in the same condition.
I'm not sure, but I think the marking is for the Nagoya arsenal.