Based on my limited research...67 was all short style and 69 was long style. Have read somewhere that 69 had a mix of long and short...whether that is true or not, I dont know...but uncles and grandfather who worked at other chrysler plants back in the day say it was not uncommon to recycle exterior parts especially body panels. A less than perfect part would not get used when the new model year was first rolling off the line...but toward the end, just before it was about to change again most of those less than perfect parts would get used rather than scraped.
Long story short...short or long style will work on either 67 or 69, but not on a 68 that has the back up light integrated into the tail light assembly