Not sure if you’re still looking for help with this or not, but I think all that is necessary is a way to set the parent post_id of the child and WP does the rest. I’m looking at this for future projects myself.
My thinking is to create an acf/save_post action http://www.advancedcustomfields.com/resources/acfsave_post/ that runs after the post has been saved and after the ACF action (priory > 10), get the value from the field and update the post to set the parent.
