We have been asked a number of times if there is such a thing as a manual disk brake conversion kit? The simple answer is yes. The power booster component almost exclusively affects how your brake pedal "feels" to you under foot.
In a situation where your classic car has multiple drivers, some of whom are used to the "foot feel" of power brakes - maybe they spend most of their time driving a newer car or light truck - a power-assisted brake pedal can makes it easier to go between vehicles. The power booster allows you to maintain relative consistency with how much pressure to apply when stopping either of the two vehicles.
You DO NOT NEED to upgrade or convert to a power assisted apply system, however, when making the upgrade to disc from drum brakes. Recently, we got an email from a customer planning on making that drum to disc brake conversion but interested in sticking with a manual set-up.
"Dave" has a '66 GTO he uses as a daily driver and wanted the enhanced performance and stopping ability of disc brakes. But as the sole driver of the car, Dave was comfortable with the pedal effort the manual brakes currently required and wanted to keep that same level of brake feel.