If your upgrading your brakes anyway, I would suggest you consider a dual circut brake master cyl - I have used a Datsun Z brake master which work very well and the dual circut brake master is much safer. Back in the 80's I used a dual circut brake master from a Ford Courier (also Mazda I believe) that worked/fit well with stock rear drum brakes, no power boost and from memory the Courier master cyl also had a built in residual preassure. Warning, brake work is not as easy as just adding new parts - I am definately no expert but do you homework. Also, the 6:1 brake pedal upgrade helps a lot IMO. The Datsun Z brake master is still readily avilable on eB.y