Kind of depends on your definition of same.
Most of the B-bodies are VERY similar across the brands. (Plymouth Belvedere/Satellite/GTX/Road Runner and Dodge Coronet/Super Bee), yet the Dodge Charger is substantially different. Of course under the sheet metal, the mechanical portions are identical.
Similarly, the two E-bodies are similar (Plymouth Barracuda and Dodge Challenger), yet not a single piece of sheet metal is interchangeable. The Challenger also has a 2 inch longer wheelbase. Again, mechanically the two are the same.
Also, you might even say that the B-bodies and E-bodies are the same. The E-bodies are merely shortened B-bodies. Same firewall and mechanical components.
So it all comes down to what you want to say constitutes “same.”
Basically I say they are the same even with those differences, as the differences are slight. I guess the most glaring difference with the Charger and RoadRunner is the wheel base or rather the ass end of the Roadrunner is longer, but to me that is a difference without a distinction.