A look inside the .zip for JRI or ECA should get you up to speed. It seems that you need these things (I haven't actually done this yet): Extra spawnspheres (obviously) Extra preview images (again...) Proper info.json (check JRI or ECA for the format). Where did you get stuck on this?
I take it you're still stuck? Open your mylevel.mis file and jungle_rock_island.mis using Notepad++ (be sure to set it to Language->JSON) and compare.