Hi Pat,
That first example that you mention, at Amberly, is of course "Hell'N Pelican II", which is owned by the "National Museum of Papua New Guinea" and awaits display there when the facility is completed.
The second example that you refer to is "Big Nig", which has been under restoration at Precision for a number of years. It was thought that it would fly when completed, and initial work was being done to make it airworthy. However, since the aircraft was obtained by the RAF Museum in 2009, the work is being finished up for static display only.
Here are some news pages that are a few years old - the aircraft is looking far more complete these days:
http://www.key.aero/view_news.asp?ID=2173&thisSection=historic
http://www.aviationmuseumguide.co.uk/news-oct-2009/news_havoc.php
The RAAF Museum, Point Cook, has a true RAAF Boston III on static display.
Kermit Weeks/Fantasy of Flight owns Howard Hughes' old executive A-20, and it is in desert storage with Aerotrader, pending future restoration.
Another A-20 Havoc which could be made to fly, is 44-0020 (N99385), owned by the Military Aircraft Restoration Company. Everything done on the restoration of the aircraft through the 90's and earl-to-mid 2000's has been to airworthy, but in recent years it has been assembled and put on static display at the Geneseo airport, likely awaiting more funding down the line to get it completed and flying.
And as mentioned already, there is the A-20 being restored at Aerotrader for Rod Lewis and will fly regularly when completed (in full stock condition).
I do think that the mention of Jerry Yagen owning an A-20 project in storage at Precision might now just be an old rumor.