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

Years ago, while at Duke Tufty Dodge in Sioux Falls SD, my parts man noticed the 1968 Parts Manual listed the 273 H/Perf. engine code for the VIN same as 1967, and here it is in my 1968 Parts Manual. Not an argument, just an interesting quirk.

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That is interesting. Notice at the bottom, N-340 and P-340 Hi-Performance.