Parts for your truck are readily available. Local Napa as suggested is a good place to start. Also LMC and some others that specialize in parts for these old trucks can help.
Stock brakes maintained properly work quite well for a stock truck. If pulling a load always allow more stopping time regardless of what braking system you have.
Or you can put disc up front, drum on back, or disc all the way around.
My 58 has stock braking system on it and stops the truck as well as my VW with disc brakes. The big disadvantage is if you break a hose or line and lose your fluid you have no brakes. Also the disc brakes cool quicker and aren't quite as prone to brake fade from heat.
But I can lock the wheels on my truck as well as I can a car with disc brakes. Just allow a little more stopping time for the sake of it. Once you're used to how they work, you'll be fine.
