What "makes" a 66 Barracuda a Formula S ??

6 leaf springs on both sides
stripes were optional, not standard and went fore/aft over the hood, roof, and trunk lid.
The exhaust has both a muffler and resonator
Until proven otherwise to me, disc brakes were not optional from the FACTORY in 1965. Dealer installed only. Factory option in 1966. 10" drums were standard on all V8's in 1966.
10" drums were standard on V/8 cars in 1965 also...