Joomla! Documentation™

1. Create and copy a link to that new 404 Article.

   Create a menu item which links to the new 404 Article and 'apply' your changes. Then copy the URL information (index.php?optio...), set the menu item as 'unpublished' and close out of the menu editing page. You may want to paste the copied URL into Notepad or somewhere accessible for the time-being.