Roadrunner or Not
So you most likely have a 318 Satellite that has been converted to a Roadrunner on some level. This means it will never be a "numbers matching" car which hurts its value from a collectors standpoint. But as a driver its value is dictated more by how correctly it was converted or how it has been modified to suit your needs.
No, it'll never be worth as much as an original Roadrunner, but that's probably to your advantage if you plan to drive it or race it. Have fun with it!