No, they aren't. They're not at all like the other true twins you mentioned.
Plymouth Roadrunner
Dodge Charger
GTX and Roadrunner are both Plymouths, just a different variation of each other. I was referring to the Dodge and Plymouth “twins”. The Charger and Roadrunner are twins, hence the Dodge Charger “Daytona” and Plymouth Roadrunner “Superbird” “twins”.
No, they aren't. They're not at all like the other true twins you mentioned.
Plymouth Roadrunner
Dodge Charger