brake upgrade questions ,Chrysler master cylinder..

[awbrown]

I am posting a pic ,it appears my truck has a Chrysler master cylinder , no proportioning valve and of course it is still drum brakes all 4 corners.. My question is this , I know Chrysler master cylinder like this were used on drum brakes , but were they used without proportioning valves??
My son had a brake line start leaking , and of course he never noticed , so I go to move the truck and the pedal goes to the floor , it still had brakes ,but the front of the master cylinder was empty .rear line was leaking .... I am no Chrysler expert so I am hoping someone here is...