It's the pitman arm; 5.75" center to center that was used for fast ratio steering. Also, shorter steering arms.
Speaking from experience, once the drive train is gone a no paperwork Z/28 will never return the investment your plan requires. Getting very tough to find AD wheels [$4,000], 837 alternator [$2,000], et cetera. Your car is very early production, finding the right dates will take years. Today, acquiring every Z-specific part the car needs represents $25k+.