I recently acquired some vintage Mustang literature and among the items was the original owner's manual for 5T09K185416. It was sold new by Wolf Motor Company in Lancaster, PA on July 9, 1965.
I searched the VIN and found some posts from April of 2010 on THE EKSCHANGE mentioning this car being offered for sale on ebay, but all of the threads are long inactive.
So the car is apparently still out there - perhaps the current owner would appreciate it being reunited with its original manual and learn some of its history as well!
Bill Collins
717-648-6600