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

I hate to say never since there was a lot of oddball stuff done back in the day, but, I've never seen a '66 Barracuda without a trip odometer......whether it was a 120, 150, tach type, etc.
The early Barracudas were very interesting cars. Many options that weren't available on other models and not tons of information about what was available.