which master would you use?

OK, I read through the old post here I think I got it but want to be sure, I am converting the front drum brakes on a 70 Duster to disc brakes from a 73 dart, so would you use the master cylinder from the 73 dart or one for the 70 Duster, as I understand it the 70 was the only year that came with the four piston brake and the 73 is single, dose that make a difference?, is the bolt pattern the same?, my thoughts are use the one for the 73 dart, BTW the car is a manual brake car and I am keeping it that way, sorry if this has been posted before I read through 6 pages of post and couldn't quite see the exact question being asked before. oh and yes I am using the proportion valve from the 73 dart to.