67 Dart disc brake conversion

I have a 67 Dart that I am converting over to front disc brakes. I have upper control arms and spindles from a 73 Duster. My question is which lower ball joint do I use. The parts places around here list 2 different ones. One for front drum brakes and another for front disc brakes. I am not sure which to use because of the conversion. I would assume the disc ones but I am not sure. The front end on this thing is going to cost me a small fortune to rebuild because it is an oddball year. And now this.