Manual Drum Brakes info needed!

Before driving my 70 dart, I've never driven a car with manual drums, so i was never sure what felt normal or not. I've always had to use all my force to get her to stop at lights and what not ( mind you I'm a very small lady so i figured I'm just weak ) I finally got my father to drive the car when he was immediately alarmed. He said the pedal felt quite stiff, and even for him it required a good amount of force to stop. He told me all the other manual drum cars he's driven never felt like this. So we proceeded to take the wheels off and inspect the brakes, they aren't worn and the adjustment on them seems fine.

My question is, could the proportioning valve cause this type of brake issue?
Thanks!!