[66Submarine]

No, you shouldn't be able to depress the pedal like power brakes; if you can, you have air in the system or other issues. It should just have a little bit of travel before going "solid". You want to generate pressure, not motion.

The one line splits and goes to both front and rear brakes. This is a modern truck from 1963, not a horse drawn buggy, lol...

If the truck is hard to stop, then look at the brakes themselves. Drums that have been turned out much will not seat up with the shoes correctly until they wear in, which could potentially take tens of thousands of miles IME. The lower shoe contact means the brakes won't be as effective.

My '65 C10 with drums that haven't been turned and good shoes stops very well with minimal effort, and will lock the wheels up easily (manual brakes, of course). It is by no means hard to stop.