Some alkaline-producing foods are relatively high in fiber compared to potatoes. Examples of relatively high-fiber foods, that are still PRAL-acceptable, are parsnips, pumpkin (but not all other winter squashes), and artichoke hearts (which I buy quartered, in cans). Such foods -- plus high-fiber or otherwise laxative fruits (prunes, cherries, berries) -- help speed passage of food through the gut. Also, I am learning to make soups and sauces from pumpkin (with garlic and lemon juice, for example).
OAT BRAN caused a rosacea/eczema type reaction on my skin when I tried the standard test (1 teaspoon/meal, for 6 meals in a row). I suspect that other forms of bran (rice, wheat) would produce the same result. Is the bran in grains a big part of what makes them acid-producing? I don't know, but I intend to continue avoiding all grains -- even white rice, the least acid-producing of all the grains.