g1smd - 10:38 pm on Aug 14, 2012 (gmt 0)
Leave the 301 in place. If it brings visitors to your site don't block them.
Google visits URLs forever irresepective of what response code you return. They do this just in case a URL ever comes back to life with real content.
The 301 is the best response. Google will drop those URLs from the SERPs eventually. Don't force a quicker drop unless you want less visitors to your site for the next three to six months.
Don't block with robots.txt or return 404.
Register every possible hostname variant (www/non-www/IP) in Webmastertools and look at the crawl stats and crawl error reports for each.