71 dart disc brake swap

1965-1972 Dart, Demon, Duster, Valiant, Scamp, and '65-'69 Barracuda are direct bolt-ons.
'73-'76 A bodies discs work also, but require use of the '73 and up upper control arm (among other tidbits) and will change your bolt pattern to 5x4.5".
'76 F/M/J body brakes will work also (edit: meant to say '76 and up), with same caveats as '73 and up A body discs (must also use late A upper control arms with the large ball joint).
Go to the "Brakes for your Classic Mopar" section of the forum and do a search. Hundreds of threads on this.
Brakes for your Classic Mopar