If you lose pressure on half your system, there will still be some pedal left to stop the car. But not much. If you set up your brake pedal to be able to utilize the full travel of the master cylinder that is as good as you can get. If your brake pedal bottoms out before the master cylinder does, you greatly limit your ability to stop when only half the system is working.
Fix all your leaks, re-bleed the system and then see how it all works out.
You will need an external 10 lb check valve on the drum brake axle if there isn't one in the master cylinder already. You will only need the 2 lb unit on the disc brake side if the master cylinder is lower in the vehicle than the disc brake calipers. The adjustable proportioning valve is a must as was previously stated.