OK, I put everything back on the time line today, synced the start points and found that after 47 minutes, the drift is 82ms not 3.4 seconds. Still large enough to hear two distinct clicks, but nowhere as bad as I originally thought. Don't know how I screwed up the original numbers.
Just received my PluralEyes software. Works great. I just threw the (3) camcorders and the board audio into vegas and let PluralEyes sync everything up. Then I went back and used Crtl/drag to adjust the end of the soundboard audio to sync with camera 1.