Parts required for swapping manual disc to power disc??

Prop valve doesn't change, though you'll want to put smaller wheel cylinders in the 10" rear drum brakes to prevent the grossly premature rear lockup the disc brake A-bodies tend to have -- it's aggravated with power brakes. See here (and threads linked from there) for details.

Booster and brackets don't have to be from a '70, you can use the easier-to-find and more compact '73-'75 item, which also gives better, less mushy pedal feel. Find a used one and send it to Booster Dewey in Portland, OR for a good rebuild ("remanufactured" items are junk).

You'll need to make new master-to-prop-valve lines because the master cylinder will move upward and forward. Don't forget to put a couple of loops in each line, as the factory did, to allow flex without metal fatigue. Get a new name-brand (Bendix, Raybestos, United) master cylinder for 1974 Dart with power disc brakes.

And you'll need a suitable vacuum tap in your intake manifold.