I'd have to say when you seriously change the body lines. I'm thinking fiberglass prostreet or funny car type bodies. Or many of the cafe racers from the 70s/80s. At those points, I believe it's more correct to say it started life as a 69 or mimics a 69. Subtle changes and refinements don't change it.
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Trey
Current rides: 2000 BMW 540i/6 and 86 C10.
Former ride: 1979 Trans Am WS6: LT1/T56, Kore 3 C5/6 brakes, BMW 18in rims
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