It was slightly work damaged left hand stopping me making barre chords that got me looking for alternatives and coming across sheet music of some Skip James songs and noting he used an extended B7 shape up and down the neck and as i can do a B7, I tried it and while I still play bad, I can play that shape anywhere on the neck and it works for me.
Graham

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http://www.soundclick.com/bands/2/grahamhenderson_music.htm