68 complete front suspension + k member on 73 duster?

You may or may not want to keep your 73 steering box. If you do, you will likely need the later model centerlink, pitman arm, and idler. Those components must go together

Lower arms are interchangeable except for the sway bar brackets

You said BBP? Does the 68 have 73/ later disk setup?
If you later go to a later/ bigger anti roll bar you may want to consider tearing that down and swapping the spindles and calipers side to side which puts the calipers in the rear of the wheels. You will need different hoses to do that