Brakes conversion, Dart 1967

it looks to me like they should have given you 3 options on the brakes - Shop By Category - Front Brakes - Disc Brake Conversions & Upgrades - option 1 is 4 piston, 2 is 3 piston and 3 is 2 piston - that one is your choice.
I don't see a "complete kit" offered - this is the booster that comes up that matches your car - Power Booster & Master Cylinder Combination - A & C Body Mopar 7 inch Booster - A28151