I do have couple of pages of original content. Around 10 pages I've are product faq's of different companies.
410 will be extreme step because I lose all PR earned as well as hit's and links to that page. I think I'll fill in my own original articles even if I add only single link text. That'd be better than a 404.
Before applying Adsense I think I should wait for 60 days after updating article with "orginal" content. May be if they check their caches and find my old copied material, it'll give bad impression.