Hello Mark,

My advice to you (as a guitarist) would be this:

Most songbooks have a chord above the words, and many a guitar chord box. What they tend to do is choose the most simple version of the chord in question - that is, one played on the first three frets. Notation composer could have a feature that added these chords. The feature could be called "suggest chord diagram", and a chord diagram would then be added above the changes in harmony.

There is no way that you could predict anything other than the most simple version of the chord. This is because other chord voicings depend on the context and style of the music. For example, as G7 for a folk song would be in open position on the first frets and a G7 in rock would be closed on the third fret, to stop the notes ringing on.

So aside from the default "suggest chord diagram", another click could link you to list of 5 or 6 alternatives that could be clicked on. I don't think you need to approach a third party, as any chord book would have these in it. By clicking on the alternative, the chosen chord would replace the simple one.

Finally, you would need to have a "custom chord diagram" option, where the composer would bring up a blank chord box, and insert dots to show where he wanted the fingers to go. This is if he was not happy with the simple chords, and the alternative suggestions were not to his liking either.

Hope this helps

Adrian