Update 5: From testing further simplifications to my method, I found that all you need to do is the map part where you must fly around until you've filled the new map(s) completely en order to get your world to convert. The chest and minecart entity stuff regarding REGULAR ITEMS do not count as far as I've discovered. This may not apply to all worlds and/or items and DOES NOT apply to oddly enchanted items(see the first screenshot for more info) and items in your inventory.