If it is a true pontiac engine built from 1968 to 1980 the intake manifold will NOT fit. However, In 1981, pontiac switched over to the Chevy engine, if that is the case then the intake manifold will work. (I do not know of any chevy 350's installed in Pontiacs though) :confused
Main difference is:
Pontiac used the same block to make the 326 all the way up to the 455, some refer to as a "mid-block"
Chevy uses the "small block" design for their 350.