there is a differance. i cant remember exactly how to word it but the disc brake master one of the resiviors is bibber than the other where the brake fluid goes. the res. for the front is bigger. on the drum drum master both are the same size.if you are mounting it under the cab in the stock location you probably will need three risidual valves i belive 2lbs presure? hopefuly someone will know the correct answere on that.hope that helps
