Jeff,I know you know most of this but for those reading , I have seen dozens and dozens of competition suspension unmolested 67 GT350/500 Shelby's with this detail and only one of maybe 4 competition suspension Mustangs with it . Partly because the competition suspension Mustang is rarer then the Shelby where it came standard. 3 of the 4 Mustangs I had checked on for this detail had been restored and had the short link. The other 1 appeared to be unaltered and had the longer link. When you ordered a link kit for a 65-67 regardless of engine size etc. you get the short length if you order 68-70 you get the longer length regardless of engine etc. which may explain shorter variations on cars that should have the longer . That same situation however would not explain the longer style on a 67 if thought changed because it would require ordering the later year link kit . With these observations over the years the most logical conclusion to me is that the longer style was typical on Mustangs with competition suspension as they are on the 67 GT350/500 Shelby's.
Thought I would add that longer
fine thread bolt needed for the longer tube end link was a 67 item (don't know if another application) because the 68-70 endlink of the same length which was standard for those years was a
coarse thread . That fact helps identify if the end link has been replaced with a typical 68-70 Mustang version. FYI I had to prove my case (a few years back) beyond a reasonable doubt with pictures etc. to a certain southern Indiana mal content
who had insisted that the Shelby bar got the typical 65-67 Mustang short end link kit .-it didn't make a difference
If you know the special one you understand why.