I study at said graduate school of said university at the moment. I do not, however study the English course. The required level of English is, as far as I know well below what you have, so there will be no need to study English. However if they need a certain score from a certain test, I guess the only thing you can do is ask them if they accept other test scores. If they do not, you better just take a test.
About the amount of study years, I think you just need to certify that you have a bachelor's or an equivalent of 16 years of study. I think none of the things are very problematic. You can contact the graduate school directly (In English it is not a problem) or the supervising professor. Is it Hall or am I mistaken?
Even though you do not need it for the program, I would suggest to you that you study all Japanese that you can. It will help you during paperwork and to find friends and so on. Good luck, maybe see you one day.