This revision (June 2015) is mostly to say that I've verified the answer by ell.  I found the Proceedings volume in question in the U. Tokyo library.  It is basically a bound volume of photocopies of handwritten notes in Japanese.  I made a "scan" with my phone, so if you want a copy of the Japanese version, just ask.  The main theorems are identical, but the arguments in the English version are substantially more detailed, and the list of references was expanded.

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Old Partial answer: You can find a copy at [one of the libraries listed here][1].  If I don't forget, I can take a look late next month when I go to U. Tokyo for a conference.  You can also [buy a copy of the proceedings][2] for 4500 Yen (plus shipping).


  [1]: http://ci.nii.ac.jp/ncid/BA63852494?l=en
  [2]: http://www.meirinkanshoten.com/book.asp?id=472611