Pitman arm issues

I have a 72 Demon that Im building. I realized the pitman arm didn't fit through the center link hole. I did have one laying around that fit perfect and had the same drop. The steering box im using is a power box . Not sure what year it is. I went to switch the pitman arms and the arm was a different size. what I need to know is do I need to change my box? Pitman arm or what. The one that works with the center link is on the left small hole. The one on right fits box but not center link.