Additional parts needed for 77 Volare disc brakes conversion to 70 Dart Kelsey Hayes disc. ??

+1 to consider the mustang rotors that @hemi71x recommended. Unless you daily drive the dart, you won't need to custom machine many rotors for the rest of the life of the car. It keeps mostly original parts and would be the way I would have gone if my car had come with original Kelsey hayes disks. Performance wise they're going to be very very similar.