Disc upgrade question...
The lines are readily available at most auto parts stores. Just make sure they understand it is for disc brakes. You already have a proportioning valve for the old drum-drum system. I'm just asking for someone to chime in to confirm whether you should swap it for a disc-drum valve. It is the device mounted to your frame rail that has the two coiled brake lines running to it from the master cylinder. It also has the single wire clipped to it that carries the signal to your "BRAKES" idiot light on the dash. When you press the brake pedal this valve "proportions" a certain amount of line pressure to the front and a different amount to the rear.