I've been rethinking the last four lines of this song after singing it to my band members last evening after practice:

We raised them old songs to the roof,
Such as shellbacks used to know,
In the good old China tea trade,
Many and many a year ago.

And I think the last three lines are "filler" which while nostalgic don't add to the song. Here's what I propose as a replacement which to me resonates more of a shanty feel:

We raised them old songs to the roof,
Like shellbacks used to shout,
As they hauled upon the haillards,
Or broke the mudhook out.

Cheerily,
Charley Noble