Which pitman arm do i get???

Ok guys, idk if this has been asked but I'm seriously at a lost! I have a 71 duster that I'm restoring and replaced the k member with one out of a 73, so I can have disk brakes and sway bar, anyways I had bought a full suspension rebuilt kit for it and got it all on the car and the power steering box was trash so I'd like to use my oem 71 steering box, and I know the sector is a different size! I have a 73 center link but a 71 manual box, my question is what pitman arm do I get??