Power steering pump/line
 

Replacing pump on 63 Fairlane 500. Can someone tell me what the line that goes into the big nut is for? The pumps
https://cimg2.ibsrv.net/gimg/www.for...4cb99f482.jpeg
https://cimg5.ibsrv.net/gimg/www.for...0ff04e5bf.jpeg
https://cimg6.ibsrv.net/gimg/www.for...5a9b413d1.jpeg
https://cimg8.ibsrv.net/gimg/www.for...6adb0d69e.jpeg
I see online do not have the center attachment, they have a solid nut, do I use the old nut? The line runs along engine and stops at throttle linkage attached to a cylinder looking part. What is the purpose of this and should I keep it? Any help with this is appreciated.