I've been coming to this site for years and have found such great information from such helpful members. I'm having trouble finding an answer to an issue I've come across. I have a 74' Nova with a front disc/rear drum set up. I'm replacing the front set up completely. I've purchased a kit from Speedway online. Master cylinder, brake booster, pads, rotors, calipers, and flex lines. The kit also included a proportioning valve. My original set up did not have this valve, however it does have a combination valve. Do I need to use both or does one or the other do the job. I'm just surprised that the original owner did not install the proportioning valve if it's required.