What’s the exact process to identify a real 66 Formula S Barracuda?

LO23M8B said
My 65 dart hipo auto had a 7 1/4 and my 66 dart hipo 4 spd had a 7 1/4 but the 66 exhaust came under the bumper no cut out. My 67 273 cuda s had a 150 speedo.

Same for the 66 Formula S, under the bumper. 67 Formula S had the large cut out.