Re: Please help on identifying rifle
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.