Like someone commented in an earlier post, the drivetrain and frame on Canadian Pontiacs and Beaumonts are Chevy, and according to the Summit site those headers will fit almost everything Chevy.
Unless someone else chimes in with firsthand experience to the contrary, I would say they will fit. That being said there is often the need for a little custom denting in some situations with these universal fit units, be it Chevy or Pontiac.

Hookers are a little overkill for a 4200 lb Pontiac    but they it sounds nice when you say its got Hookers     Hedman or any generic header would be a better deal $$$$$