Roadrunner or Not
This may be one of those deals where one of the previous owners wrecked the RR and cloned it with a Belvedere/Satelite and didn't use the original RR vin/data plate, back in the 70's & up it was sometimes necessary to use a donor and keep the donor title to match the car body to prevent trouble with the law.
In California, if you don't have a vin number when/if your pulled over your car would be impounded, after it gets sorted out the CHP will issue a new vin tag number and install it in several places.
Anyhow, that is a great looking car.