I just did the spocalc thing and found that the difference at the rear is < 1mm and between front and minimum rear is 2mm - very small differences. I respoked/re-rimmed NR-hubbed wheels several times long ago and I think I used the same length spokes everywhere and remember filing them to shorten them a bit sometimes (probably on the freewheel side). Does this sound crazy? Are the exact lengths really that critical? +/-2mm is a range < 3/16"