Engine size for 57 Pontiac

Answer 1

Factory engine size in the 1957 Pontiac was the 347. Mine has a V8 283, so they must have supplied different stock engines in different models.
Of course, mine is a Canadian car and, I hear, one of the very few left.

ALL U.S. Pontiac for 1957 had the 347. Canadian Pontiacs in the 1950's-until the mid 1970's were rebodied Chevrolets, and thus equipped with Chevrolet engines. Pontiacs built for Canada also had different trim, names, etc. For example the Bonneville was known as the Parisienne in Canada, and was identical to the Chevrolet caprice under the sheet metal. The midsize Pontiac in the US was the Tempest/Lemans/GTO in Canada it was known as the Beaumont and was identical to the Chevelle under the skin, including Chevrolet engines.