There are 2 books out there that are the "bible" for the WF's:
-- Paul Schmid, "The Experts Book"
-- Martin A. Armstrong, "Washington Franklin's 1909-23 (I think 23)"
I've had them both, but lost my Armstrong. The reason why I like the Armstrong book, is that it is like reading a story-- it takes you through the history of each issue, and you end up with a pretty good understanding of why each issue happened, and it's just a fabulous book.
From your original question, I can't recommend this book more strongly for you. It is out of print, it's paperback, and you can find it sometimes on eBay
, or from any of the philatelic literature dealers out there.
Good luck, and if you find mine, please read it and return it! :)
Hope this helps, Ray