Swapping in a Pontiac 350/389/400/455 in place of a 301 is easy to do. It is a very popular swap since there is virtually no aftermarket for the 301.

Pontiac made "Bandit" versions of the Trans Am from 1977 all the way into 1984. The original "Bandit" movie car was actually a 1976 Trans Am with a pre-production 1977 front clip. The movie was filmed before the 1977 models were being built. There were 3 "Bandit" movies. The first used the 1976 T/A with the pre-prod front end, The second movie used a 1980 Turbo T/A, and the last one (without Burt) used a 1983 T/A. (The last movie was really bad with Jerry Reed "faking" he was the Bandit.)
The Body style of the Firebirds from 1970 thru 1981 was the same with only changes to the nose and tail thru the years. The body style change over was the 1982 Firebird.

The 326 Pontiac was not of the same block design as the other Pontiac V-8's.
It was actually designed by Buick.