Asking an hourly worker at a place like Autozone to get marine parts? Good luck! The statement "a deer in headlights" is an understatement. If it's not right there on their screen, forget about it. It's like asking a McDonald's cashier to manually make change! Now, some NAPA stores can help, though. But even that's hit or miss.
A local Mercruiser shop can help you. They can figure out what you need based on the year. FYI, many things on a sterndrive engine are "marine" specific and are specifically designed to be "ignition protected". Meaning, using automotive parts can make your boat go BOOM. Plugs and wires are fine to swap - cap is not. Alternator, starter - don't even think about it.
Dont forget to check/replace the impeller for good measure. And, absolutely check the condition of the bellows - unless you don't mind the possibility of your boat sinking