If I block SE's with Robots.txt and reuse content will it be seen a duplicate?

I had an old site that was hacked and has a bad backlink profile, so I've killed that site but it's a good adsense earner.. 2k per month from that 1 site. I have started a new site just like it but have not launched it yet because the old site is still indexed in Google. I've deleted the old site completely from hosting, only leaving the robots.txt file, and have deleted the domain name. I heard it takes months for Google to deindex a site. I will be submitting all the URL's from my site to be removed in Google Webmaster Tools, but that also takes a while to be processed.

How can I get my new site up and running without worrying about duplicate content? Some of you guys churning and burning must not be waiting months for old sites to be de-indexed?

Thanks

I just helped another person with the exact same problem as I had the same problem before. These are the steps you want to follow to be able to reuse the content:
1- Delete the content from the urls, update and ping if you can.
2- Delete the URLS (but make sure to save them in some .txt or whatever), update and ping again.
3- Upload a robot.txt with the disallow code so robots do not crawl your site.
4- Go to your GWM account and submit the URLs you have deleted to the deindex part of GWM.
5- One last ping to make things faster.

After you have done that, you are good to re-use the content. Now bear in mind it will still show in copyscape for a while, but this does not matter as it is just part of the internal cache and you have already deleted the real thing.

Thanks. What is the best way to ping?

And doesn't Google have it in the internal cache and can still see the content even thought robots is blocking the actual site? Meaning they can see the old and new content?

bumping this once