4 wheel disc brake using stock MC

Not sure if this helps but I am running the Factory M/C on a front disc 72 B-Body with added (97 Jeep Grand Cherokee) rear disc on 8.25 rear. I added a Summit prop valve and it has worked great. I didn't have one but have read that there is a restrictor in the rear orefice of the Disc/Drum M/C that you should remove.
Try it. Can always swap out later. I also wondered if you could remove the factory prop valve when using an adjustable. Why not?