Problem with Prop Valve/Metering Block

Running rebuilt power booster/mast cyl with single piston discs and 10" drums, all new lines, and original brass prop valve/block. When I bleed the brakes, the front does fine, but don't get anything out the back. I loosen the fitting on the rear outlet of the prop valve, and its bone dry, so I am not getting anything across it. I disassembled the prop valve and cleaned it real good. All the springs and seals and such look fine, actually look brand new. Any ideas? Any chance, I assembled something wrong? Seems like it can only go together one way. I would appreciate any advice. Thanks.