Looks like a Type 99 Arisaka that someone tried to sporterize. They were popular with the old Enfield and Springfields as barrel guns ($15-25) for deer hunting after the war. Look up on the web and there are many pictures to compare it to.
I don't have any ammo and don't believe my pap modified this at all. I just assumed with the Japanese's writing on the stock, it was the way he found it.
I'd love to shoot it but I believe those days are long gone for this gun. I've had it since the mid 80's and it looks the same. Wish i would have gotten the story behind him acquiring it though.
I got one similar when my dad passed. It was a 7.7 with a steel butt plate. We shot it when we were younger. Man did that thing kick. My dad thought you could shoot U.S. ammo through it but our guns would not shoot their 7.7 Nothing I ever tried to prove though