To be 100% certain you need a build sheet...
The VIN may be on the engine/trans but the engine/trans could have been swapped... So that proves nothing... The Fender Tag has the SO number same as the body... It will have the first few digits of the VIN but not the last six.. It will have the SO number so if the Fender Tag shows the RM designation & the SO number matches you know it started life as a Road Runner... Hopefully as the same Road Runner the VIN came on.

"The Armies of our ancestors were lucky, in that they were not trailed by a second army of pencil pushers."