Clear up something in the original trans-am cars?

Tidbit from Camaros.org forum
-The SCCA allowed the 302 Chevy in the Firebird because the Chevy engine was used in some Pontiacs in Canada. 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.
.....and elsewhere -The Sports Car Club of America’s Trans Am Series racing was extremely competitive during 1970. The Big Three, as well as American Motors, had a factory-backed racecar in the series. SCCA homologation rules dictate that in order to race in the series, production versions of the racers have to be produced.