Hi Owen,
I was looking at this example that story map team has created, it is great!
http://storymaps.esri.com/stories/LandsatCompare/
I want to know if this map was made using is an ArcGIS online template? and if so how do we add the sources for left and right
maps like you have here:

Is there an option to that while configuration of the app or you had to do some customization or code to do that.
Thanks for the help.