Be careful of your alternator too, I got some degreaser seeped into my rear alternator bearing and it ran the bearing dry and started making cracking noises unbelievably loud afterwards. Otherwise, yes, you can just SLAM that thing with a pressure washer, I do it monthly now, its pretty easy to not get the alternator DRENCHED without really trying, over spray is fine, water won't really hurt it either, just be sure not to get degreaser in the bearings.
If the alternator is dirty, parts stores sell cans of electrical parts cleaner, usually made to clean up alternators specially and make em all clean, but usually not an issue. The quickest and easiest way to do it is to drive it over to one of those pressure washer DIY car washes, then get the engine nice and wet, soak it in degreaser, bring a toothbrush, they're very helpful, you can then also hit it with the wash solution they have on hand and then just BLAST it clean. Don't worry about getting ANYTHING else wet, get the WHOLE engine bay clean. Just make sure not to get an open K&N wet, and you're good to go.
Fair warning tho, there is good chance that once you start, you may not wanna stop until its perfect