If you rebuild the stock system properly you will be fine. These cars stopped good when they came from the factory. If you want discs, an all new kit is the way to go, but as Bob pointed out, it won't be cheap. As far as using a junk yard donor car, good luck finding one. Even if you do, the parts will probably be spent. You'd be better off to just rebuild the 4x drum system in my opinion. Make sure to get new rubber brake lines. I've seen where the original factory clamp on them was crimped on too tight, causing a restriction... and making the car to pull to one side.