Take your dad's '57 Caddy with 4-wheel Bendix drum/shoe brakes. Undo the vacuum source to it's Bendix Hydro-Vac Power Brake Booster, and see how she stops now.
To answer your question, adding a booster should aid significantly in pushing the pedal down, possibly to the point of making the brakes very "touchy" if the system was not designed to use a booster. Boosters can aid in multiplying foot pressure dramatically. DD