If one's going to cite examples it's as well to check one's sources first, John hill . . . Going to the Mudcat archive, "Shoals of Herring" has:

As we hunted for

For to go and hunt

And I'd dream about

That we'd taken from

While you're searching for

As you're following the

We were sailing after

which is as I remember the song, and all seems grammatically correct and ship-shape. In fact MacColl was generally meticulous over such matters . . .

However this - and too much of the discussion above - misses the point ENTIRELY. There isn't a single "grammar"; a grammar can just as well define a language (or more usually a dialect) as it is actually spoken, as define how a language "should" be spoken.

Of course there is a (not entirely precisely) defined grammer for contemporary UK English, and s slightly different and no better defined one for US English (in the UK we DON'T accept "leverage" as a verb!!). If you're a teacher, or are at pains to appear "educated", then this matters . . otherwise it's a question of personal taste . .

Equally "of course" - if you're not happy with the words of a song you're free to change them . . .

The Radio Ballads (for which "Shoals of Herring" was written) probably illustrate this . . . without checking I'd say the series includes a lot of grammatical examples, in its field recordings, which don't match the BBC's accepted grammar of that time (which, of course, is different from the BBC's accepted grammar of today).

G.