The zillionth excellent history from you.
I grew up about 70 miles from Waycross GA, where Parsons spent most of his youth (and which he once referred to as "the armpit of the south"). The Atlanta college radio station where I dj'ed briefly circa 1969 had a copy of "Safe at Home" (I haven't seen one since--should have pilfered it) and the Sweetheart-era Byrds (which would have included Parsons) played at my college. I think (but this is shabby memory) McGuinn kept the vocals.
A lot of folks contrast Parsons with Gene Clark (whom you've also profiled), but I think the two country-rock pioneers are different enough to merit their own individual pedestals in the pantheon.
In case you don't know it, here is the wonderful Swede pop sister duo First Aid Kit singing "Emmy Lou" to Emmy Lou Harris: at the Polar Music Prize celebration: https://youtu.be/Y3TzP-o4vhs