1 vent hole over the chamber is 99
2 vents is type 38.
OK, back to the tizzy fest that I started by accident about dust covers: I found my IJA-issue small arms manual. I will see if they have a maintenance section that will probably deal with dissassembly. The manual is not specific to the rifles only, so I may have nothing.
Does anyone know the actual Japanese word or kanji for the dust cover. Being an official manual, they will certainly not say "just take that thing off whenever and wherever you want."
However, if they do make explicit mention that one should not the importance of not losing the dust cover, it would be interesting. Also, if they specifically warn against throwing it away, we can assume that people threw them away.
I'm completely willing to admit that I have MUCH less knowledge concerning Arisakas than a truly dedicated and well-read collector.