mine has a buick 5,7 (350) engine.
and i believe it is the original one.
seems you can keep them apart by the place of the distributor.
front or back of the block. (they told me
mine is sitting in front. very close to the water hose connection.
i had a 76 or 77 coupe with a 400 pontiac engine. (not sure if it was original)
for what i know there are different engines used in bonnevilles thrue out the years.
offcourse due to emission and oil crisis in the 70'*.
please DO correct me if i'm wrong ...