It was on a Chevelle. The nuts only had hold of maybe four threads, tops, of course no cotter pins.....which is why I was brought the car. He wanted to know why he couldn't get the cotter pins in. lol
Yeah, it's not the "wrong" steering linkage. If anything, the 73+ linkage usually creates MORE space, not less. You certainly have no way to guarantee that switching over to the 67-72 linkage will fix the problem.
TTI lists the headers as fitting 67-76 A-bodies with stock steering components, it doesn't say they won't fit with the 73+ steering linkage. And using the '73+ linkage on a 68-72 K-frame doesn't change the position of the linkage.