"Modest Maid of Kent" is in my broadside index, ZN1349, and it was sung to "Languishing Swain". C. M. Simpon in 'The British Broadside Ballad and Its Music' #183, 184, discusses the tune at length, (under He that loves best must suffer most) but the upshot is that there are two possibilites, but no solid identification of the original tune. There are folksongs that were originally sung to the tune, also, "Grazer's Daughter/ Betsy was a Beauty fair" (Laws M20) was originally the two part ballad "Love Overthrown + Constancy Lamented" (ZN2523 & ZN46). "Early, early in the spring" (Laws M1) is "The Seaman's Complaint" (ZN2863). Laws P33 was also (the earlier version) to the tune.

The broadside ballads cited here all seem to be of 1690 or at most a few years later.