I'm posting the corrections (TY Jim)to the excellent minor version sung by Mrs. York in 1940 which would make an excellent starting point for a ballad cover by someone like the talented Brian Peters.

Pretty Polly (corrected) Sung by Mrs. James York 1940, NC.

Come along Pretty Polly and go with me
Before we get married a friend to see.

He led her o'er hills and valleys so deep,
At last this poor damsel began to weep.

Oh William, I'm fearful you are leading me astray,
One purpose my innocent life to betray.

Come on Pretty Polly you guessed it just right
I was digging your grave the one part of last night

Her lily-white hands in horror she rose
A-crying for mercy: What have I done?

They went a bit further and what did they spy
But a grave ready dug and a spade by the side

She threw her arms 'round him and suffered no fear,
How can you kill a girl who loves you so dear?

Come on Pretty Polly, no time to stand,
He instantly drew a large knife in his hand.

He stabbed her through the heart and the blood it did flow,
And into the grave that poor body did go.

He threw some dust o'er and turned to go home
Left nothing but the birds to make a sad moan.

Oh where is Pretty Polly, oh where is she?
Oh, now I am bound for one part of the sea.

It should be commented that both Mrs York and her husband James were excellent singers, collected ballads locally and in her case, she got version from both her parents.