4-Door with 340 from the factory?

Pretty sure 350 4 barrel gm B/O/P engines could have dual exhaust.
Especially in mid sized cars.

Mom's buick lesabre was 350-4 but single exhaust.
Neighbors olds cutlass was 350-4 but duals.

...and pretty sure a lid with a 455-4 sticker could have been picked up at a junk yard for less than $5 back then.