Absolutely sure. next to an unaltered arisaka, the chamber is noticeably cut back/shorter and has a gap in the wood.
I took it back to the LGS and they tried to run .308 in it but the bolt wouldn't close. So it's very likely 300savage (they didn't have any on hand.)
So unfortunately, I have $400 wall art.
At least it has a good stock (maybe original) and aircraft sights and a monopod. Now I just need to find an intact-mum type 99 nagoya of the same series and build my own mixmaster.