importing the Island to mod

I made a few mods to train.

I want to upgrade a bit, by modding on the Original Island.

My problem is how I can best import the Island map, everything. Landscape, spawns, weather etc.
Is there a way to import it the right way? (because my pc takes a LONG time doing landscape jobs)

I would like to mod the Original Island, pre-snow biome with the obelisks in their original place.
Is there a location where the Original Island is stored?