Re: Ď68: Brake distribution block Q.
Hi. What you are thinking of is a Combination valve, and it sounds like you have the stock distribution block.
To answer your main question first - yes, if you have the stock distribution block on your car, it is just a distribution block with a provision for a brake light indicator in case either the front or rear brakes lose pressure. In your case, it sounds like it was stuck, so most likely only 1/2 of your brakes (either front or rear) were working properly.
Now, back to your first thoughts - a disc/drum Combination valve has 3 parts - a Metering valve, a Distribution block and a Proportioning valve. The Metering valve does exactly what you were thinking - under light braking, it will delay the front brakes slightly so the rear drums have a chance to start kicking in. The Distribution block part does the same function as the stock distribution block and blocks off one or the other if the opposite system (front or rear) loses pressure and grounds the brake light indicator. And the Proportioning valve part biases less pressure to the rear brakes to prevent the from locking up before the fronts do.
Before combination valves came into being, these three parts were carried out by three different components.
Note that on a disc/disc Combination valve, the front Metering valve is eliminated.
1972 Chevelle, 454, 2004r non-lockup, 4.10
1981 Camaro Z28, 355, TH350, 3.73