As for "harpoon", I've always assumed the same as Little Hawk -- KK needed another syllable. "Harpoon" isn't all that much different than other screwed up words that permeate lyrics (especially folk!) in an effort to make the rhythm or rhyme come out right.

Either that, or that's just the way he said the word to himself, like how I always refer to my friend Joyce as "Joysarooni" in my head.