Yes, the adjustable proportioning valve is all you need to control the pressure to the rears. That part must be called a "metering valve" somewhere like GM world. Prop valves were never built into Mopar MC's. You don't require a residual valve for the rear drums. Those went away long ago when they changed to a cupped spring in wheel cylinders.
When you install your dual MC, you must re-plumb. In my 65 Dart, I re-puposed the factory "distribution block" (tee) for just the front tubes, by blocking the rear port and installing a 1/4" M to 3/16" F inverted flare adapter. Your new MC will have 3/16" tubes, not the big 1/4" tube of your factory single MC. I used a 3/16" inv flare union to connect to the factory rear tube. You can find these parts in the bubble packs at Autozone. Do not install a 3/16" tube into the top port of your distribution block (without above adapter). I know you can find tubing nuts that fit, but it will not seal correctly.
Many choices in MC. I think all 4-bolt ones are cast iron. You can get a firewall adapter to use a 2-bolt aluminum one. I used the booster & MC from a ~95 Breeze w/ ABS, but you don't require power brakes in an A, even with front disks. If you get too new, you run into bubble flare ports, which are harder to make (see youtube).
