The National Library of Scotland was the partner on this project and also offers them in easier to locate format at http://www.nls.uk/family-history/directories/post-office.The NLS will be offering an online index at some point, using the first three letters of each surname. There is already an index online for the Glasgow editions, pulled together by a University of Strathclyde student, Michael Tobias - for more, see http://scottishancestry.blogspot.com/2010/12/scottish-directories-project.htmlBrilliant resource!
Thanks for the update, Chris! I agree they are a brilliant resource.
Sorry, just twigged these are additional books - good find!