Don't throw any brake parts away. Even if everything is rusty, most will be reusable after blasting in your new cabinet. You'll probably replace the shoes, but if you can find a place to reline your current shoes, even better. You will replace the springs. But if the cylinders can be blasted clean, honed to clean up without pits, then for sure just buy a cup and bellows kit. The result will be much better than the screwy new castings that the current cylinders have.