Saying a sweep is 'black as soot' is silly. And adding 'I'm sure' just to make it rhyme is feeble. Ask yourself - what is this comparison with a Moor supposed to imply? Just that he's dirty? Or more than that: unpleasant? frightful? Personally I'd leave it alone.

But changing the 'came' of DT to 'come' is an improvement IMO.