Clear up something in the original trans-am cars?

THIS: "In 1970 the rules changed and the SCCA allowed them to de-stroke the factory engine so the 1970 Z/28 and Javelin and Mopar did not have to have a 305 limit on the factory built models."

That is why Chrysler did not field a factory team until 1970. The various independent Dart and Barracuda entries prior to 1970 used 273s, and thus were at a serious disadvantage.