I have a 1969 PC50 and I've noticed that the brakes are awful. I've replace the pads already and they are still sub-par.
I've sanded down the drums and pads and cleaned everything with brake parts cleaner. I got a big improvement by adjusting the brake arm on the hub so that the brake cable attached at a right angle, but they are still sub-standard.
How are your brakes? Have you figured out any way of getting them to perform better?