It makes sense to work backwards from rock to folk by listening to groups like the Grateful Dead and Ian & Sylvia. "Dead Reckoning" is a must. It is in several topic threads on Mudcat, and it includes at least six traditional folk songs, including "Jackaroe", a variant of a Child ballad. "Sing Out!" and "Rise Up Singing" are being recomended to you because they are political. Following that approach would put you in the deepest rut in all of music.