The steering box attaches, via the pitman arm and the relay rod, to the near side hub. A relay rod connects the nearside hub to the offside hub. You adjust the length of the relay rod to change the tracking.
To adjust the position of the steering wheel, you put the wheels in a straight ahead position. You then disconnect the pitman arm from the relay rod and you then centre the steering box by turning the steering wheel from max. one way to max. the other and then turning it until it is in a central position. Now remove the pitman arm and refit so that it re-connects to the relay rod. Finally remove and re-centre the steering wheel if necessary.
As the pump is the original to your motor, it is unlikely to be the problem re: heavy steering. I suggest you measure the slack at the steering wheel in the straight ahead position---this is the position of max. wear---and again at full turn left and right. If it tightens as you turn, it may be because someone has tightened the adjuster nut to try and compensate for wear.
Roger