I agree with you! The purpose of the check valves is to prevent fluid from draining from the wheels back to the master. If your wheel cylinders and calipers are below your master there’s no need for them.
You didn’t say what Master cylinder you’re running. Ford had several masters with different sized reservoirs. If you have one like discribed you are probably good not using a proportioning valve.
like the ole saying goes “If it ain’t broke don’t fix it”.

Call them. I’m pretty sure they have a Non Power set up too.

on another note how far are you from Bently MI. THERE’s a 56 Cab & Frame for sell there.

About residual pressure valves - it is critical to have one with drum brakes. The design of wheel cylinder cups makes them seal more efficiently as pressure in the system increases because the sides of the cup are forced tightly against the bore of the cylinder by the hydraulic pressure. Conversely, if the pressure drops all the way to zero, they won’t seal well at all and the brake fluid can creep past them and leak into the brake mechanism. The primary purpose of the RPV with drum brakes is to maintain a small pressure on the line at all times to keep the cups sealed to the bore when the system is at rest. Whether it’s the rubber duck bill under the seat in the master cylinder or a separate inline unit, you have to have an RPV or you’ll have fluid-soaked brake shoes in a short time.

Regarding the proportioning valve, most originally equipped disk/drum vehicles use a combination valve. The combination valve is comprised of three sections - the proportioning valve, the metering valve, and a pressure differential valve. As was mentioned, the prop valve cuts the pressure back to the rear brakes. Adjustable versions are readily available for dialing in mixed systems. The differential valve mostly just flags the idiot light on the dash if there is a loss of pressure in one half the system and isn’t critical to have. The metering valve, on the other hand, often gets overlooked. It holds pressure back on the disks up front until the drums in the rear start building pressure. That’s important as it helps keep the back end from coming around during a hard stop. I’d definitely look into adding one in. The easiest way is with an aftermarket combination valve.