Lighthouse, I don't know that Roger McGuinn was ever a part of the NY Folk scene. He hailed from Chicago and studied there at the Old Town School, and I do believe spent some time around Columbia University, but I don't know if he was a participant in the Greenwich scene with PP&M, Dylan, and the Mugwump offshoots. I think McGuinn moved to LA early on when he spent time in a duo(believe it or not) with Bobby Darin.

Since the Byrds came to the forefront of the new Folk/Rock movement in early 65, at the same time as Barry McGuire, my guess is that the two served as examples of the "Commercial success" that was suddenly available to folkies.

Still not sure what "Duffy's good vibrations" alludes to in the last verse.