I don't think the meaning of the word matters. It would be nice to know, but it's unlikely you'll reach a conclusion, though looking at other versions sounds like a great idea. IMO all that's important is that we enjoy the song.

I like it because it's quirky and has an interesting feel to it. I think it's definitely bawdy: even the line, 'as I take a long stick in my hand' potentially has a double meaning.

I looked in an etymological dictionary (yeah, another librarian I'm afraid) and there were no clues there. Doldrums is related to the word 'dull', but I mean... 18 inches!!? Long hair (dull and shabby looking) sounds like a good interpretation to me.