pitman arm help?

i have a 70-71 duster with manual steering and i swapped the k member and disk brakes from a 73 duster and when i ordered all my tie rods, ball joints, idler arm and pitman arm i ordered them for the 73. now the problem... the 73 pitman arm wont fit my 70-71 steering box splines because the arm hole is to small, but from what ive read im confused because some say the 73 box had the bigger shaft and some say the pre-73 had it and others say there are three sector shaft sizes lol. which pitman arm do i need to order? have the moog pitman arm for the 73 but its to small. do i need the pre-73?