That's how most of us slant-6 freaks do it, because most of us find that's the way that gives the best results. It's not the only possible method of getting a satisfactory adjustment, though. You're wise to raise an eyebrow at methods that are high-handedly professed to be uniformly best for any/all solid-lifter engines; optimal procedures vary widely across different engines with different adjustable valvetrains. It's your decision, of course.
BTW, those Chinese-made chrome valve covers are problematic and it looks like yours may not be set up correctly with respect to the PCV—which will louse up your idle quality and create other problems. See Thread 1Thread 2Thread 3. If you are bound and determined to keep this valve cover on your engine, and if you can make the bolt holes line up, then set up the breather and PCV this way.
