Tony- not an expert on these- military Serial numbers are not always unique- some repeated. The Mum being intact usually denotes a rifle captured in combat. Those surrendered at the end of the war had the Mum ground off (or defaced) to avoid shaming the emperor.
In general terms, a military rifle that has been sporterized now has a value as a shooter, not as a collectable- although some may be restorable, depending on the metal work done to it. The Arisaka has a rep as a strong action, 6.5 Jap is findable, but no longer cheap (milsurp ammo went away) recoil mild.
There will also likely be arsenal markings indicating which arsenal made it. Like THESE: Markings on Japanese Arisaka Rifles and Bayonets of World War II