Hi -
the phrase in question is:

I'll do what is right or I'm not from Cape Cod,
I'm Jack the cantankerous cuss from Cape Cod.

It's an interesting idiomatic construction that's fairly common in American English.

I can't recall any other examples right off. Maybe something like:

I can catch a shark in my bare hands,
Or I'm not Barnacle Bob the Sailor.
I'm Barnacle Bob the Sailor.

(apologies to Barnacle Bill)

Here's a recording of "The Ballad of Mad Jack":

https://www.youtube.com/watch?v=h2sBJx-bnTQ

(may not be playable in Europe)

-Joe-