Id also be interested, you said rotors have to be milled down for axles? or stock rotors work? any special prop valve needed? have 73 and up style on the front and drums out back but id like to ditch the drums and go 4 wheel disc....
The center register in the rotor needs to be opened up .04 of an inch to clear the axle register. Basically a stock mustang rotor.
You can use a prop valve if you want, but since you have disc on the front already than your master cylinder will still work because the proportion is already built in. The front brakes do all the work. The rear just helps finish it off, the master cylinder does not know if its drum or disc in the rear. It just supplies the same amount of fluid.
I originally ran a manual 15/16 bore master cylinder from a 90s dakota.
Now I am running a hydroboost system from a 05 ish diesel ram with 1 1/8 bore master from a 92 ram van.
The problem with mopar rear disc is the parking brake shoes. I detest those and have only ever had issues with them on my dakotas, rams, sebrings, intrepid and the charger. I always get them seizing and locking up the brakes. Besides that style of brake was not designed by mopar anyways. It's a system prepared for them by another company and bolted on.