while attaching my centerlink on my 68 back in i noticed where it attaches to the idler arm there is 1/4 inch between the arm and the centerlink and that is with the castle nut on there so i can get a cotter pin in the hole. just wondering if i need to tighten so the arm and link touch or just so i can get the cotter pin in the castle nut?

Rick, it's good that there is some room between the arm itself and the center link, otherwise there would be rubbing when you turn the steering. The stud is tapered and can only go so far that taper of the stud fits the taper in the center link. Make sure the castle nut is reasonably tight when you put the cotter key in though.

Sometimes those came with a foam rubber washer to take up that space, helps to keep debris out of the joint and grease in.

Jeff