Well, this may not be suitable as a top level comment, if so I'm happy to delete. My advice would be to read books or short stories written in that time period and set in said period. That's likely to have the smallest possible amount of anachronistic language use.

This image post shows anachronism in works set during WWI. The bottom left was written in 1919 and hence held to be essentially true to the time, as a work written in 2009 set in 2004 would be. Really this ties to what I said above, read contemporary literature like The Great Gatsby, [Manhattan Transfer](http://en.wikipedia.org/wiki/Manhattan_Transfer_(novel)), or The Age of Innocence. That will likely give the best feel as to the accurate vernacular.

I really doubt that somebody from that era would have used mother fucker as the expression was from the 1960s. Probably the best source would be either Norman Mailer's war novel "The Naked and the Dead" but ignore "fug" or James Jones "From Here to Eternity"