According to this VA Mustang blog and many other examples I've seen, there are 2 holes where the bumper "could" be installed. Am I missing something? I did see in the other thread pictures you posted of plates with no holes so maybe they made 2 styles? http://blog.virginiaclassicmustang.com/2012/10/new-65-70-mustang-rear-end-pinion.html?m=1
Yes there is an earlier and later - at least at San Jose for 65 and likely at the other two plants though the change over took place at different times. All depends on where and when the specific car was built. The link shows the "new" reproduction of the later version with the three holes that I mentioned just recently in the 65 Dearborn discussion on the subject and pictures of the earlier version with the single hole were posted there too. Have not found any NJ examples to post as of yet to this thread.
If you notice in the link their research shows the change taking place in April 65, six months after when your car was likely built, but they don't state which plant but guessing that's not NJ
Just to confirm since the angle is not the best to see the detail. Your reporting that you car has the larger/longer version of the snubber plate where the forward edge of the plate extends to and over the main floor section of the undersides?
Don't seem to I have any real clear pictures of other October built 65 NJ since those cars are in short supply in decent condition. Need more examples to help determine what and when things took place for K codes at NJ