I found FLEX Overpass, but not FLEX Viaduct. I tried using the overpass for it but it didn't really work the way I wanted it to... though to be fair the elevation on this map is completely messed up too (I ran out of patience when trying to generate a heightmap with the Tangram Heighmapper and repeatedly importing them with SC4Mapper - SC4Terraformer seems to not work on Linux at all so I had to just import it over and over and hope half the city isn't flooded or that the sea isn't land