73 Manual Disc/drum Master cyl no residual valve

I have never seen a residual valve either, but perhaps they were only in disk/drum cars. As stated, the metal cups on the ends of the wheel cylinder springs supports the rubber cups, eliminating the need for a residual valve. Sometimes the spring wire is wound to form a "cup" for same effect.

All MC's I have seen have the same bore for front & rear brakes, so the pressure is the same up to the "imbalance switch" which lights the warning lamp if not true (when it works). The prop valve then reduces pressure to the rear drums (if front disk car). Both are in the factory "combination valve", along with a "hold-off valve" on the fronts.

I bought 2 adjustable prop valves for <$30 ea on ebay in last few years.