I had a go at this a while back, it just seemed like a good idea, but gave up after getting repeated crashes. Look at the thread
http://www.subsim.com/radioroom/show...ight=type+1939 there is a lot of information provided by people who have done it, warning!! there are a lot of files to mess with.
Cheers and good luck May and Lex A search on "XXI in 1939" will also find it