Originally Posted by Jim K
It looks like a Type 99, BUT has the sling attachment of a WWII German Mauser. AFAIK, no Japanese rifle ever had that type of setup. And yes, I am aware of the Siamese Mauser and the Type I, both of which have sling swivels.
So either the rifle was built with parts of other rifles or is an oddity. Better pictures, closeups of the action, markings, and the sling setup are needed.
Would need better pictures, but the Arisaka carbines had that type of setup (side sling) and towards the end of the war, all kinds of variants were being cobbled together. Better pics would tell, but if there are no screw holes on the bottom of the buttstock, this long rifle likely came this way.