https://books.google.com/books?id=Pe5mAAAAcAAJ Referenced in GF's journal
https://babel.hathitrust.org/cgi/pt?id=hvd.32044081817447;view=1up;seq=7
quoted in Jaffray introduction by Barclay, maybe not written by a friend, but looks pretty interesting
Truth's Innocency and Simplicity Shining through the Conversion ... (With the Long and Patient Sufferings) of that Ancient and Faithful Minister and Servant of Jesus Christ. http://digitalcommons.georgefox.edu/quakerbooks/7/ is only a partial copy... John Barclay speaks highly of him. Would be worth trying to find a full copy somewhere and digitize if necessary. Doesn't seem to be a google books version or archive.org available.
Referenced in his journal. Short and pretty good: https://catalog.hathitrust.org/Record/011609217
https://books.google.com/books/about/A_Collection_of_the_Epistles_and_Works_o.html?id=XDJxvqIRTw4C