Is my car a Tag Job? Barracuda Decode...

As I’m sure you know, you had to order the disc brakes and 8 3/4” rear end separate, they were always an extra cost option and never part of the FS package
Oh sure, but, those options mentioned are quite common along with the FS package. Just getting a 273 4bbl and a tach without it being a FS is fairly rare. Of the six '66 FS's I've owned (4 auto's, 2 4 speeds), all had disc brakes, and only one (an automatic) didn't have an 8 3/4. My non-FS car has all that gear too, along with the heavy duty suspension and heater delete. Strange car. I also had another non-FS one that was a 273 2bbl, 4 speed, 8 3/4, and drum brakes. Another oddball.