Yes, you can sub cornmeal for polenta and I wouldn't sub the Masa harina because of the lime.
polenta = mush Pronunciation: puh-LEN-tah Notes: This Italian specialty is made of cornmeal that's been cooked into a thick mush. The mush is either served hot, much as Americans would serve mashed potatoes, or it's cooled, sliced, and then fried, grilled, or baked. It's easy to make at home, or you can get tubes of ready-made polenta in the refrigerated section of many supermarkets.
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