Hi, Richie
I'm coming more round to the idea that the story is based as Fowler says. The oldest looking broadside is your Boston one and c1730 seems like a reasonable date now. I very much doubt if the BCY imprints are any earlier than 1740. The style of printing on their sheets always makes me think 1750-1800.

A good hack of around 1730 could easily have heard the story of the murdered girl at Gosport and decided to marry this with the well-known Jonah tales. The writer of Bramble Briar at about the same time did a similar thing with the Isabella story and gave it a local setting in Bridgwater.