You want 7/8" rear wheel cylinders and this: https://www.ebay.com/itm/NEW-Mopar-A-bod...E/173718540627?

As stated above the 4 wheel drum block is a distribution block not a proportioning valve and I would also take the rear adjusting valve out, if it was my car. The proportioning valve will bolt right into place on your 70 if the factory lines are still present.

If the pedal is still too hard for your taste you can play around with master cylinder bore size. maybe go up to a 1" or 1 1/32" bore.