The photos are showing the stock setup, the proportioning valve is integrated into the distro block / brake warning light block.
Earlier years 67 till that went with single piston 72-73??? Was set up that the MC lines went to the distro / brake warning light block. The the rear line went out to the proportioning valve then to the rear end.
IMHO you would want the proportioning valve after the distro block IF it has a brake warning light in it. Other wise you will be feeding one side of the brake warning system with higher pressure then the other and the light will come on at every brake.
