Kelsey Hayes disk brake conversion question

The lower ball joint(LBJ) and steering arm come as a one piece unit. The LBJ installs into the LCA (Lower Control Arm), and bolts onto the spindle.

You may not need a Comination Valve with 9 inch drums on the back. A Combination-Valve is a Proportioning-Valve with an integral Differential Pressure Warning Safety Switch.
You may not need the Metering Block either (separate item).

I have neither a C-valve, nor a M block,with the same front brake set-up, and 10inchers on the rear, but with 275 tires.I imagine the Proportioning Valve might be needed with 205s back there,maybe. But I imagine,with anything else, and 9inchers the P-Valve would probably be optional. I would certainly try it without the P-valve
The Differential Pressure Safety Switch is a good idea, but more for it's practical way to handle plumbing from the dual reservoir M/C, than for it's ability to tell you about a hydraulic problem. The M/C should have a Residual Valve in the rear brake circuit, but NOT in the front circuit.