All Pontiac motors from 1964- 1977 were big block motors. Including, 326,350,389,400,421,428,455. They are all big blocks and all have interchangable parts. Some 1978's had big blocks but most in that year were victims of the emissions change over. 401 oldsmobiles and some other crappy chevy motors.
I have spent lots of time with Pontiacs, just love the way they drive!