Is it possible to search Wikipedia including deleted text

I'm afraid there's not any way to do this using the API or anything like that. However, you could probably do something with the Wikimedia dumps to find the sort of duplication you're looking for. The people already doing research might also be able to help you out.

I made such a tool. It's a bookmarklet that generates the references in a single click.

You can find it here: https://en.wikipedia.org/wiki/User:Ark25/RefScript

It works with the following newspapers: BBC, Daily Mail, Daily Mirror, The Daily Telegraph, Huffington Post, Huffington Post Canada, The New York Times, The Washington Post, The Boston Globe, The Times of India, Financial Times, The Economist, Wall Street Journal, Business Week, Ars Technica, TG Daily

The problem (for me) is that I have to teach the script how to handle each website. Another problem the newspapers change their formatting of their pages sometimes, and then I have to update the script. If there would be a W3C standard for presenting the four required fields: title, date of publication, names of the authors and name of the publication, then the script would be much shorter, won't require updates and it would work with any publication that implements the standard.

You can support my request for implementing such a standard here: https://meta.wikimedia.org/wiki/Talk:Community_Engagement_%28Product%29/Process_ideas#Make_life_easier_for_the_editors_-_generate_references_in_one_click

Also check this question: https://webapps.stackexchange.com/questions/59231/unified-standard-for-publication-date-and-author-name-in-newspaper-articles