I picked up a Hal Leonard How to Set Up the Best Sounding Banjo by Roger Siminoff for $16.95 (US) about a year ago. Not being a banjo player, I can't say how helpful it would be to you. My interest was general instrument construction, and it did have some interesting stuff in that area.

I would expect that you'll find more pertinent information at the web site above, but it might be something that would be of general interest if you happen to run into it - A place to pick up some "theories" that people who play can refute?

John