castor setting is more important than centering the axle in my eyes.
remember, the axle doesnt travel strait up and down, rather, it travels in a radius. if the control arms are stock length, when compressed, the tire will be centered in the axle as it travels through its range of motion and reaches stock ride height, and further compresses. with longer control arms, your going to be stretching the width to begin with, and youll start running into rubbing with larger tires at full compression in the fender well. control arm drop brackets are intended to flatten the angle of the control arms at ride height... though you may get a little stretch...
as far as adjustable arms... most people do adjustable uppers, rather than lowers, as this makes it easier to adjust castor without effecting the wheel base a ton. at your height, stock length arms are fine, whats really important is that the lowers have a bend in them or the axle side bushing is offset so that the arm doesnt contact the shock mounts when drooped. for reference, my RE super flex arms are stock length lower, and just a hair longer than stock uppers, which i assume is to accomodate for better castor. of course, they are beef, which we all love.
