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

Hyper_pak said
Wow, I really thought they had a code for the 273-4. Learned something today.
My friends 66 S had a 4 speed console. Inland shifter POS, but had the console.
Light Gold, in and out, no stripe, front disks and 8 3/4.

67 had a different engine code for 273 4 barrel, as did 68 but I have never seen a 68 273 4 barrel.