Japanese DVD

It is indeed open matte. If you blow it up on your TV, an equal part of the top and bottom are matted out. However, this doesn't mean you're seeing the widescreen version the director envisioned. When a movie is (hard) matted, varying amounts of the top or bottom are matted out. In each shot the director chooses the frame he thinks is best. As a result, in some shots for instance 20% of the bottom and 5% of the top are cropped, whereas in other shots 10% of the bottom and 15% of the top are cropped. Although by blowing up you may be seeing it in the right aspect ratio, you don't necessarily see the "correct" widescreen version.
Whenever split-screens appear, the movie presentation switches from open matte to letterboxed widescreen. I don't know if you're aware of the split-screens in this movie. They were very popular in the seventies (and now again in series like "24"). During a split-screen you are seeing simultaneously two, three or four screens, which are placed side-to-side or on top of each other. The screens are placed in the middle of the picture with black bars on the top and bottom. In this case, your blowing up will work properly, as an equal part of the top and bottom will disappear. You also may be lucky with the Japanese subtitles. As they are placed at the bottom of the picture, you may be losing them along with the bottom part (as they are burned-in, they also stay where they are and don't move up). The only thing I'm not sure about is if by blowing up you're really losing only from the top and bottom. On some TV systems you're also losing from the sides.
I knew this movie in a 2 hour version that was shown here in Europe on TV. The 143 min version is quite interesting, although towards the end the additions drag the movie a little bit out IMO, but someone else might feel different about this. I haven't watched the 104 min version yet but sure will do.
Hope this helps!