Thanks to the questionably-canon Hyrule Encyclopedia (currently Japan-only), we do have at least one interesting real world material, the above screenshot. That's all we get it seems, which is unfortunate, but still, a neat look at what would have been the level select screen before they implemented an overworld. An old Iwata Asks on Spirit Tracks sheds light on this; scroll down a bit and you'll see a sketch that looks similar to this image.
It's not much, but it's very cool to see this piece of history surface after more than 30 years, and thought it was worth sharing with the community.