Converting to rear disc brakes questions.

I have a 73 Duster with manual front disc and rear drums. I am contemplating converting the rear drum brakes to disc and I have some questions.

1) Do I also have to convert to power to be able to apply enough braking force?
2) Can I use the same master cylinder?
3) Do I need to install a proportioning valve for the rear discs?

Thanks for the input!