I came across this board mention of George Benson Fox's letters. I have had them all digitized and you can find them here:

https://app.box.com/s/q9hjrs6bleispmps79b33imhepxxj039?fbclid=IwAR2_7q8oRMTnP-djV4fSwZxNHCKUqQEjafQONrklSXn7k-HAB-x6QAilAkU