This recipe is written for a 9-by-5-inch loaf pan and yields a nicely-sized loaf of pumpkin bread that is domed over the top rim once baked. I would hesitate to use a much smaller loaf pan (like an 8-by 4-inch) as you may risk a spillover in your oven, but an 8.5-by-4.5-inch loaf pan would likely be fine, with an increased bake time to account for the extra height. You can place a rimmed sheet pan underneath the loaf pan if you're concerned about spillover while baking.