Anyone use a QA1 K member on a 74 Duster

Yep they sure are different part numbers, and this corresponds to the 73 up centerlink and large sector shaft 73 up power steering box (different spline count and larger diameter) because of this and how the pitman arm is shaped along with spline count, if using the 73 up steering box, you will have have to use the 73-76 pitman arm, requiring you to use the 73 up idler arm, center link, and inner and outer tie rods.

The idler arm mount on the k frame however is the same from 68-76, and the steering box location is the same from 67-76.

As long as your using the entire steering gear setup. Idler arm, center link, pitman arm and steering box inner and outer tie rods from the 73-76 it's a direct bolt in on a 68-72 k frame.

adjusting sleeves are the same from 67-76

What you cannot do and make it work is mix 67-72 and 73-76 center links pitman arms, idler arms tierod ends and steering boxes.