I believe the Tamiya Musashi kit represents her more-or-less as built, whereas the Yamato kit represents her in her final configuration (or nearly so). The latter involves a huge increase in the anti-aircraft battery, including an extension of the superstructure on several levels on each side. (The Musashi kit's maindeck looks remarkably bare by comparison.) What Tamiya did with the two kits, in other words, is quite similar to what was done to the real ships. Actually the differences between the two actual vessels were minimal. They're described in the Janos Skulski's outstanding book, Anatomy of the Ship: The Battleship Yamato. Skulski also describes the modifications that were made to both ships - including the addition of the port and starboard 6" turrets late in the war.
The Musashi kit, in other words, could stand in as a reasonably accurate model of the Yamato in her original configuration - and the real Musashi, just before she was sunk, looked a great deal like the Tamiya Yamato kit.
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