Sorting photos manually and keeping that sort order when exported

I have 330 photos in an album on my Mac. I sorted them manually. When I select these 320 pictures and export them to a folder on my desktop my sort order is gone and they are now sorted by the file name. How can I keep the order that I created in photos in the folder on my desktop?

If that is possible it might solve my problem because I want to upload these pictures to Shutterfly to create a photo book but Shutterfly sorts them by date or filename which is the wrong order.

Is there a way to automatically give these pictures a name or number that can be used to sort them?