The 289 and 302 are identical exterior wise, after all the 302 is a stroked 289. They switched to the 302 during the '68 model year and some motors, like the 289 in my '68, have a 302 block.
In 1968 the 289 would be a "C" as the 5th digit in the VIN. The 302 would be a "J", and the 390 would be a "S". There were a handful of '68's custom ordered with the 2v 390 and they were "X" codes since this option didn't show up on the sheets. If the VIN is an 'S' then the car was originally a 390 that at some point was replaced with a 302 or 289. Not uncommon for vehicles of this age to no longer have the original motors.
There was no such thing as a fastback convertible. On the driver's door data plate the first code is the body style.
'63' was for a fastback. There would be a letter after the number denoting what trim level it was, A, B, C, or D. A was for standard interior, B was deluxe interior, C was standard interior with a front bench seat, and D was deluxe interior with a front bench seat.
'76' was for the convertibles.
Where did you get the VIN from when you sent it in to Ford? Do all the VINs match on the car? The one on the driver's door, the front windshield, and the inner fenders. It's possible the driver's door was replaced at some point with a door from another car but they left the tag for the other car on. It's also possible the inner fenders were replaced showing a different VIN. There's even the remote chance someone put all the VIN identification from another car on this one for some reason. That's why the VIN doesn't match what the car is. The only VIN requiring much work is the inner fenders, the other two only rivet in place. While theft could be one reason for this, I know of people who have switched VINs (although illegal) because of lost titles or other paperwork. They would buy a wreck or a parts car with good paperwork and swap everything with another vehicle. While this would work with the DMV it would create a problem if the car is researched through Ford or Marti and it comes back as something different.
__________________ 1968 Mustang coupe, Acapulco Blue, 289 2v, C-4, Power Steering.
Hopefully a 1969 convertible or Sportsroof (non Mach or Boss) for next Mustang project 
Trying to find my father's 1973 Mustang Grande he bought brand new. 3F04F126773 last known registration and title was in New Jersey, 1982. | 
