Disc brake conversion (70 Dart)

Well for one thing those are 73 up, "B' body pin type calipers in your picture, that won't work on an A body car, due to the fact where the rubber flex hose, brake line attaches to the caliper.
There have been dozens and dozens of threads on these disc brake conversions, and what to do, use, for the conversion.
Use the search feature on this forum, and GOOGLE will also be your friend.
And those upper control arms won't work either.
They are 73 up, B body UCA's.
You found a "B" body set of brakes.