If your master cylinder(MC) is original then you will want to put a brick or a short piece of a 2x4 UNDER the brake pedal to prevent the piston in the MC from traveling too far and tearing the rubber diaphram. That area is not usually traveled and rust develops. When the rusted area of the piston travels past the rubber diaphram, it will tear the inner ring of the seal causing "blow by" when braking, giving you a soft pedal and poor stopping performance.

The other is to make sure you use a FLARE NUT wrench for the copper lines going to the caliper. Don't try to use a regular open end wrench on the soft fittings.
You may want to soak the fittings with penetrant first for a couple of days before attempting to crack loose the fittings.