I have a Nagoya type 99, I don't know how to tell if it's a series 6. But it has a ground mum. I have 3 others but I don't know enough about the markings to say for sure what they are. I know one is a Toyo Kogyo, the other 2 are either Koshikawa or Kokura. The markings look the same to me, I'm definately not an expert on Jap rifles. 3 are carbines, one is long. I have 2 more that I got in a trade years ago that came to me taken apart in a box, they are still in the box, somewhere. I will find them and see if I can identify them. These are the only Arisakas I've had and never paid much attention to them because I don't know anything about them. If anybody knows about these I would buy you dinner or cook you a steak if you would come look at them and share your knowledge.