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

cosgig said
The Formula S was primarily a handling package, brought about by the Rallye Pack option from early 65. It consists of….

HD leaf springs, 6 leaves on the passenger side, 5 on the drivers side
Click to expand...

I'm pretty sure 66 up had 6 leaf springs on both sides. I know a "67" 4 speed Formula S 273 and "68" auto Formula S 383 both had 6 leaves on both sides. I never had a 65 Formula S.