Can you interchange a 1973 Plymouth bumper with 1975 duster bumper?

No, you cannot directly interchange a 1973 Plymouth bumper with a 1975 Duster bumper. While both are Mopar products and from a similar era, the body styles changed significantly enough between 1973 and 1975 that the bumpers are not compatible. The mounting points, overall dimensions, and even the bumper's shape itself would be different.