Nice idea. Don't you think Mexico should border Central US?
Actually, I've just made a different variant. Unlike the last version, this one uses only direct connections, without the need for some board-to-board crossovers to take two moves.
The positioning of Mexico was a problem that kept bothering me because, at first glance, it looks like the two halves of the country can simply click together because they're the same size. Then I compared the Global 1940 map to the Anniversary Edition map and I realized that, in Global, a vertical strip is missing from the middle of North America (which helps to explain why British Columbia and Ontario practically touch each other). So the fact that the two halves of Mexico look as if they are connectable is just an illusion. That's why, in the new variant I made, I decided to extend the border of SZ 10 all the way to the land spur at the bottom left of Southeast Mexico: because there's a missing strip of land between the two boards. It's a better match with the official rules too.
Comparing Global with the Anniversary map also highlighted for me just how big the difference is in the scales between the two halves of North America in Global. Another thing I found surprising when I compared the maps was that the Global rules say that SZ 51 is adjacent to SZ 64, 65, and 66. SZ 51 only takes up about 20% of the height of the map, while SZ 64, 65 and 66 add up to about 45% of the height of the map, so the Global rules connect two boards in a way that implies a huge height difference between the two sides. In the new variant I made, I disconnected SZ 51 from SZ 64, so that the height difference wouldn't be quite so extreme.