Greg, of course Dylan MAY have been familiar with "Arthur McBride" at age 21 or 22, I just don't think it very likely. He was't really into much Irish stuff outside of the Clancys (he learned "Brennan on Moor" from them and used that tune, for "Rambling, Gambling Willie", if memory serves). I don't think they ever sang "McBride": probably because they didn't know it either! (I knew Dylan recorded the song in the 90s, I have the album). Masters of War tune is based on Nottamun Town, learned from Martin Carthy, allegedly.