For this box to work with your stock front center link, you need to use the stock pitman arm from the donor fbody or, use a stock 67-69 power steering pitman arm-either will work on the later style fbody boxes.
The 3rd gen f-body pitman arm will not work with a 1st gen f-body. It is completely different. Use the correct year P/S pitman arm for the car that the box is going into.