Your observation is one way you determine that the car is a factory GT, the fenders' MUSTANGS letters are crooked. All three of my San Jose Fastback GTs (1 1965, 2 1966) are that way. Because of all the croocked letters, I would think that the holes were hand drilled using a paper template or a worn metal one. It fits the way you determine if a Rally Pak is original Ford, the clock don't work.
Jim