Brake problems

As I understand them, the only thing which can restrict flow to the front circuit is the "metering valve", which I think is the left screw-on in the photo of post #6. Its purpose is to block flow to the fronts until some pressure has built up to assure the rear shoes are contacting. If it was stuck shut, you would never get flow to the front. It might be removable. You can find posts w/ cutaway views & explanation here. If you already re-installed it, I would just try blowing it clear by standing on the pedal w/ both feet. All rust problems disappeared since I changed to DOT 5 long ago in all my non-ABS cars.