1970 El Camino Brake Question

I’m working on my 70 with factory disc brakes up front and drums in the rear. I’m in the process of replacing the master cylinder along with the booster. The prior owner installed an adjustable proportioning valve, which I will be replacing with a CPP (PV4) proportioning valve. I bought the PV4 because I’m also installing a CPP rear disc brake conversion kit. My question has to do with the factory distribution valve mounted to the frame. Does the PV4 valve replace the distribution valve or do I need them both?

The CPP valve will replace the metering valve down on the rail and bolt up on the rail as well.

Thank you for all the replies. I’m beginning to think this is going to be a bigger job then I planned. I understand the new proportioning valve (PV4) will replace the original distribution block mounted on the frame. As for the pressure hold back valve some have mentioned, I found it, it’s mounted on the drivers side above the axle tube. I’m assuming this valve needs to be removed when I install the rear disc brake conversion, correct? If it does need to be removed can I replace it with a threaded coupler or do I need to replace the entire brake line?

Thanks again for all your help.

threaded coupler would be fine.