Thank you for showing the scale. What tool do you use to measure and draw that block? Uber Cool!The show building of Disneyland's Runaway Railway takes up about 1.75 acres.
Tokyo is more than capable of getting MMRR but the better question is how eager they are to get it.
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The entire neighborhood section of Tokyo Disneyland's Toontown would have to come down to make way for the building. Before the massive Fantasy Springs expansion, they could have put the MMRR showbuilding behind Toontown, just like Disneyland but that ship has long since sailed.
Another major factor that would likely discourage Tokyo from building MMRR in their Toontown is its ridesystem. On the left side of the picture is Pooh and on the right is Beauty and the Beast, two trackless attractions. MMRR would be the 3rd trackless attraction in just that specific spot.
was my guess of the small world building being about the same size? Now that I see your overlay I am guess the small world is a little bit bigger.