Probably be easier for you to not use the stock power booster brake set-up and go with a unit that is close to the newer disc/drum set-up - what about the brake booster set-up from your parts truck that will are least get you in the ball park for the disc brakes. You will need a proportional valve also designed for disc/drum balance. You're dealing with a lot of mismatched units that will need a little engineering balance.