Roadrunner or Not
The good news in all of this is you probably are in possession of a real 1968 383 4 speed Roadrunner. The problem is the title you have is not for that car, the title you have is not for any car. The real VIN might be stamped on the drivers side trunk lip under the weather strip.
It is possible that there was a typo in making a title at some point but that doesn't explain why somebody fabricated a VIN stamping to match that where a VIN stamping wouldn't have existed.
The good news in all of this is you probably are in possession of a real 1968 383 4 speed Roadrunner. The problem is the title you have is not for that car, the title you have is not for any car. The real VIN might be stamped on the drivers side trunk lip under the weather strip.
It is possible that there was a typo in making a title at some point but that doesn't explain why somebody fabricated a VIN stamping to match that where a VIN stamping wouldn't have existed.