One of the most important things to do when switching from power assisted brakes to full manual is to change the pedal ratio. Often the correct mounting position for the pushrod for manual brake master is already in the pedal from the factory. Factory ratio for power assisted brakes will run in the 3:1 to 4:1 ratio. You will need a ratio of 6:1 or even 7:1 to be able to apply the manual brakes using a moderate force from "leg power". If the pedal ratio isn't changed; you may need to use both feet to get enough force applied to the master cylinder to stop at a reasonable distance. The above is correct for either disc/disc, disc/drum and drum/drum manual setups. Using the correct master is also important. A disc/disc setup will require a master with large reservoirs to supply the calipers. In all variations the master cylinder bore size will be smaller than what would have been utilized for power assisted brakes. You should be considering a maximum of a 1" bore or possibly as small as 3/4" for the manual brake setup. For power assisted setups a 1 1/8" bore will work better.
Because some readers will look at this posting but be considering going from manual brakes to power assisted setups; I am adding that going in the reverse of the above info would apply for them. They would be looking at a slightly larger bore master and the pedal ratio around 4:1 and a booster with a minimum size of a dual diaphragm 7" (not much boost with that size though). A larger 8" dual diaphragm would be a better choice.