4) Late-model cars are now equipped with diagonally split master cylinders, which means each reservoir has two ports. The bottom ports (to the rear drums) have large, residual check valves, while the top ports go to the front discs. The diagonally split system is used on front-wheel drive cars, where 85 percent of braking is done with the front wheels. For greater braking capability (as opposed to a front-to-rear split), one front and one rear wheel will always be stopping the car.
5) You can tell by the bumps in the lid which chamber is larger. The chamber nearest the mounting face is for front disc brakes (larger chamber), and can also be used for front drum brakes by removing the residual check valve.
6) Adapters shown on the end of the two brake lines (and in the outlet ports) will be needed, since the ports are larger than the 3/8-24 brake line fitting. The right port is 1/2-20 thread, while the left port is 7/16 - 24.
7) Before 1968, the residual check valve was in the cylinder bore, and disassembly was required for its removal when used for disc brake applications (arrow). Afterwards, the check valves (two assemblies at the bottom of the photo) were placed in the outlet ports behind the visible, brass inverted flare seats for the brake lines, and can now be easily removed with a small screw, shown on one of the inverted flares.
8) The deep pushrod hole on the right is for manual pushrods, while the left, shallow hole works with power boosters. Be sure and check this when buying a new master cylinder.