Thanks, Stuart, that's all very interesting. You're right about Mary Barton, too.

John Harland and T.T. Wilkinson's Ballads and Songs of Lancashire, from the 1880s, includes a version very like the broadside I linked above, but in stronger dialect. It was collected 'from the singing of an old hand-loom weaver at Droylsden' and - according to Harland - written just after the battle of Waterloo. Harland wrote that it was 'still a favourite in many parts of Lancashire'.

Comparing these texts with the folk revival version, it's clear that a skillful piece of re-writing has been carried out. As Richard Mellish points out, the stanzas have been reduced from six lines to four, but some of the surplus phrases from lines 5 & 6 ("He ne'er picked o'er in his life"; "I've woven myself to th' far end") have been accommodated by repeating the opening lines ("I'm a four loom weaver as many's the man knows / I've nowt to eat, and I've wore out my clothes") and making two new verses. Five of the old verses have been cut.

The pious and complacent parson's role ("We should have better times if I'd hold my tongue") is re-allocated to 'Bill O' Bent', who appears in the broadside as a debtor.

The closing lines:
"Hoo's nowt agen th' king, but hoo likes a fair thing
And hoo says hoo can tell when hoo's hurt"

have disappeared, leaving the verse to end on the less conciliatory:

"Hoo swears hoo would fight, blood up to the een"
('Hoo = 'She' in Lancashire dialect, of course)

Harland tells us that those last three lines were 'household words' at the time of his publication.

Which still leaves the mystery of when the ballad was re-written, and by whom!