"It should be noted that in those days, "blow meant knock."

Wrong, there were many meanings attached to 'blow' by mid-19th c.

1. stolen goods- "He has bit the blow" means he has stolen the goods.
2. to smoke- How the swell funks his blower...
3. To blow the gab- to confess
4. To blow the groundsils- To lie with a woman (on the ground). A nautical usage.
A few of the many slang terms meaning 'to knock down':
( I'll lump your jolly nob for you- I'll give you a knock on the head.)
(To lace- to beat.)
(To floor- to knock down).
(And on 'knock,' some meanings already prevalent in 1785-
To knock- To have sexual intercourse with a woman.
A knock me down- strong ale or beer.

From the OED:
1. to blow- to be winded. From 1440 (in print)
2. To blow (the bellows) - to stir up passion. 1596
3. To blow- to sound (an instrument)- 16th c.
4. To blow- to scold or rant at. 1827
5. To blow- to drink to excess. 1500
6. To stroke, to hit. 16th c.
7. To bloom- to flower. 18th c.
8. A blow- A storm. 17th c.

In various nautical works-
To blow- to raise the sails
(As in this 19th c. version of "Blow the Man Down:"

So we'll blow the man up, and we'll blow the man down.
To me ...
And we'll blow him away into Liverpool Town.
Oh gimme ...

I'll post the rest of that chantey when I run down the reference again. Also see version 3 in the DT; a late one but echoes the meaning of an earlier one- I've got to get busy on these.

The Black Ball chantey or an early version is a 'boasting' song. The line as commonly spoken of was re-organized in 1835, and that is the one sung about.