Re: adjustable gas block
You'll most likely never need an adjustable.
Times when you might want one would be suppressed, or if you just want to load singles without the additional semi-auto recoil impulse. The rifle as a whole will also benefit from a regulated gas system if you're running overly hot loads.
Different mfg's attach gas blocks differently. Some are pinned and require the use of a punch. Others use set screws or tension bolts to hold the block in place.
Not rocket surgery to change one out. Proper alignment over the gas port is as hard as it gets. If it doubles as a sight base, plumb in the vertical as well.