Hejsan, there fore it´s neccessary to know that this beautiful song isn´t an american one, it´s a scottish song.
By reading the lyrics you might understand ...( Clyde is a river in scotland )
But now to the question wich chords to use.
I play it in "D minor", but its just my own oppinion ´bout a song sounds and therefore I prefer the version by Paul Weller.
Dm, Bb, C, A,
             Bb    C                  Dm
Black is the collour of my true love´s hair
             Bb    C            A
her lips are like    some roses fair
             Bb          C                  Dm
she has the sweetest smile and the gentliest hands
            Bb   C            Dm
I love the ground whereon she stands


It maybe hasn´t no more that touch of a traditional folk song but I like that best reasonly by the story of that song.
Mostly it sounds to happy, she´s waitin´for her LOVE coming back home from war, there´s fear and hope, sadness and the knowledge ´bout she´ll never live on when he´s dead......YEAH! THAT´S A LOVE SONG ISN´T IT?"