I absolutely love Nora Brown. 🙂 She has a great collection of old time tunes in both clawhammer and two finger styles. She’s certainly wise beyond her years in old time music.
Clawhammer is my go to style, but I got to know Matt Brown a couple of years ago and probably actually play more two finger songs than clawhammer these days. He actually has a new 2F book coming out really soon.
The Leftwich book is really good, in my opinion. It focuses specially on musicians from the Round Peak area in North Carolina, so many of the songs are familiar, but they’re regional variants of the songs.