I'm also starting to explore this area because my '51 4400 seems to have the same setup as yours. Mine isn't even a roller yet, so I'm hoping to learn from other people's experiences.
What happens if you disconnect the line to the wiper motor? Basically return to the original setup.
Also, as I understand it, the reservoir is designed to give you at least one assisted stop even if all vacuum is cut off to it, as if the engine dies. After that the brake pedal just gets a lot harder to push, but the brakes still work.
Does any of this sound reasonable?
