They don't. After you either change the K or modify yours to take a 68 or later idler arm, there are 4 pieces that must match each other, independent of a 68/ later K
The pitman arm must match the steering box spline. There are large and small splines. If you end up with a 73/ later center link, you must use 73/ later pitman and idler arm, as the studs on them point the opposite direction of 72/ earlier.
The only other "thing" is whether you are going to use a factory anti-sway bar. 72/ earlier mounts under the K, and uses different lower LCA tabs than the 73/ later bar, which goes INSIDE the K member.
