How could I adapt this to use a loaf pan or standard cake pan?

I've had success with halving the Sunset Whole Orange Cake on this site (and of course, Sunset Magazine) and baking in a loaf pan. If it's because you don't have a bundt pan, you can rig one with a wide round cake pan and a narrow, oven safe glass and lots of aluminum foil, but it'll look pretty janky. Loaves should be fine. It seems pretty dense, so I wouldn't try baking it as rounds.

The recipe is written for a tube pan or similar type (such as a Bundt pan), so you should be able to do it in a narrow loaf pan (0r pans) with appropriate capacity (10 cups). An adaptation could probably be made for a standard cake pan, but it would be tricky, as the proportion of surface area to volume would be much lower; this would particularly impact the glaze, but would also affect the overall baking time and final texture of the cake. Unless you're in the mood for some science experiments (which by their nature include a good chance of failure), it would probably be best not to. I might recommend a similar cake (without buttermilk) from the same book (New Book of Great desserts) called "The Best Damn Lemon Cake", which is designed for a 6 cup loaf pan.