I agree with Dale's synopsis. The Auto Pact was phased in over time. Production was already committed by the carmakers and they would need a little time to adjust. It lead to a dropping of the A51 Sports Option Malibu SS & Sport Deluxe after the 1st quarter of '67 production & adding the Chevelle SS396 & SD396 Sport Deluxe models, plus buckets & console as freestanding options. I can also add that basically for every car built in the U.S. & sold new in Canada, one had to be built in Canada & shipped to the U.S. Initially the new  Ste. Therese, Quebec plant built U.S. spec Chevies exclusively for export to the U.S. starting with the 1966 models. They were painted in lacquer with black firewalls & spatter paint trunks and carried a "6" alongside the paint code. Meanwhile Oshawa used enamel paint through the 1968 models, with body coloured firewall & trunk, and a "9" alongside the paint code.

Starting with the '69 models, Pontiac brought in the GTO as a mainstream offering. With luxury & performance image preceding it, the car was expensive to buy & insure and was for the well-heeled Doctor. Enter the 1969 Beaumont SD-396. Available only on base cars with cheap seats & rubber flooring, it was GM Canada's answer to a cheap affordable performance car to compete with the Road Runner, Super Bee, and now Torino Cobra & even the 300-Deluxe SS396. 1969 marked the start of GM Canada offering numerous axle ratios as offered in the U.S, not the assigned ratio as generally it had been in Canada up to then. The Beaumont wasn't to last, as the Le Mans would start to roll off the line in Oshawa for 1970. If your car didn't have any special need to come from the U.S. & was running a 350, you would get a Chevrolet 350 with a Pontiac 350 decal on the air cleaner. Back then the basic question when buying a battery or parts was, "Orange block or blue block?" As in Chevy or Pontiac power.