I recently installed a new rear end into my '78 Malibu. The new rear end came with 11" disc brakes, but the car itself came with front disc and rear drums from factory. I ran into issues using the stock proportioning valve and master cylinder. After searching around online, there are proportioning valves marketed towards disc/disc conversions, claiming that is the only mod you need, while others say you also need a different master cylinder. Is it possible to get away with just a new proportioning valve and a stock master?