If you remove one side of the linkage on the brake drum, then apply both brakes, you can check the linkage rod length compared to where the brake shoes stop.
What is probably happening is one shoe hits before the other and you only get 1/2 the stopping power. My bet is you will shorten the linkage rod.
If you're interested , you can re-arc the brake shoes so they contact fully with the drum. You spray glue sandpaper to the inside of the brake hub-220 grit.
Lightly apply the brakes as you turn them inside the hub. Remove and you will see the high spots. Keep turning and applying until you have full contact. Vacuum up the dust with a good vacuum, wear a mask. Old brake shoes may contain asbestos. If this scares you, there are brake and clutch companies that can do this process.