The thing you removed is not a proportioning valve. It's just a distribution block with a pressure switch that controls the brake warning light. It does look similar to the switch/proportioning valve that came with your disc kit, but it doesn't have the proportioning function. The proportioning valve reduces the pressure to the rear drums during hard braking to compensate for the different braking characteristics between disc and drum. This keeps your rear brakes from locking up. It's not needed or desired for drum/drum brakes.