Yes, I had forgotten about the 1748 ballad entry but I don't have access to this being on the wrong side of the pond. Presumably it is just a list of first lines but there is a strong probability it is our ballad, the other 2 being later. A more useful piece of info would have been a title. All of our titles other than the 1800/1830 broadsides are editorial. Pitts was in direct line of descent from the Dicey-Marshall dynasty of printers who started out in the early 18th century. The Diceys would have been favourites for having printed the earliest version and not everything of theirs has survived. The ballads of this era tended to have longer more descriptive titles. I have 2 Dicey catalogues 1754 and 1764 but no Gallant Ship. If we had an original title that would be a start.

The Fanning Manuscript version of 1779 also in Cambridge Mass. but at the American Antiquarian Society, differs very little from other versions (no title) even to the extent 50 guns 550 men, Orange, Looe and Unity.

A close search through the ECCO songsters might throw up something but I haven't got time at the moment.