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

For me me I see people at swapmeet claiming they are selling formula s cars I check the lower control arms if the have sway bar tabs welded on them. Them after check the rearend for the 8.75 depending on year I don't think 64 came with the 8 3/4. Also another way is checking the rim width. But then again all this stuff can be changed around over the last 50 years lol. So vin and vin stampings would be the best way but depending on year I think later barracudas had multiple stampings on the body of car, I don't know about early ones maybe they have one at the rad and not at the trunk.