For 68, any "P" code(5th digit on vin) is a Formula S. All 340 68 cudas were an S. Obviously the 5th digit being H(383) is a S as well.
S'cuder abv nailed it. Post pics.
My 69 S ragtop was 4spd, std brakes, std str, no tach and 120 speedo. Drum brakes all around. Plain Jane lol