Percy's Song is on Mudcatthread.cfm?threadid=55316#859909
I remember the Fairport Convention recording of it. They may have been drawn, as I was, to the tradional-sounding "turn, turn to the wind and the rain" refrain.
Here is a version of Child 10 (Twa Sisters, Binnorie) with a similar refrain @displaysong.cfm?SongID=4372

The lyrics do sound like they could be about a friend of Dylan's.

Percy's Song doesnt sound like the version of Hiram Hubbard I used to sing, no great similarity except that the song is also about someone wrongly accused "Hiram Hubbard is not guilty, I heard the people say/He was not in this country, he was many miles away" Of course there may be another version which has a similar tune to Percy's Song for all I know.