1) The Sports Car Club of America (SCCA) races classic Camaros, Mustangs and other muscle cars. May be the same category or classification as Trans-Am, I don't know the exact details.
2) Back in the '60s-70s, factory speedometers on most American cars went up to 100-130mph (161-210kph). It is easy to re-gear the final drive for a different top speed, but the speedometer showed the same numbers. There is no "correct" top speed since you could bury the speedometer with some bolt-on power adders (supercharger, header/exhaust, etc).
Those are my educated guesstimations.