Robert -
Why not make each of the "-" representing the tongue equal one hole blocked?
As in:
D-A D--BD D---D
etc.
I have a tab font, Chromatic Sans Dot, that does a similar thing vertically (has to be vertical as it's for placing under notation; the version you use below is more literal in its alignment if not its spacing).
By the way, I'm overing a similar subject in a series of articles at harmonicasessions.com.
WinslowBb-----Gb,Bb A--------F,A Ab-------F,Ab G--------E,G Gb------Eb,Gb F--------D,F E,G-------E Eb,Gb-----Eb D,F--------D Db,F------Db C,E--------C B,D--------B to Bb------Gb,Bb
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