REAR END SWAP QUESTION?

I HAVE A 72 CHARGER WITH A 318 AND 727 AND P245/60R14 TIRES.
IM NOT SURE WHAT REAR END I HAVE, IM GOING TO HAVE TO LOOK.
ID LIKE TO GET MORE POWER BY CHANGING REAR ENDS AND WAS WANTING TO KNOW WHAT REAR END I NEED AND OUT OF WHAT VEHICLE.
AND IS THERE A NEWER ONE WITH DISC BRAKES TO LOOK FOR?
THANKS FOR ANY INFO
Author: THE GOOSE