Upgrade to Dual Braking System

56 Plymouth. Where do I even begin to upgrade the single system to dual?? Or, should I just make sure all my lines are in good condition and live with it?

It made it 50 years so far. Make sure what you have is in good condition. Watch out for hidden rust.

BTW duel systems are not 100%. I lost a seal on one side, and hit the brake harder only to blow out the duel in the Pennsylvania mountains.

I would have more faith in Plymouth’s system (if in top shape) than in my home-made dual system.

There are aftermarket conversion kits for some cars, with Chevies of the early '60s one example for which I have seen ads.

Do yourself a favor and buy a copy of Hemmings Motor News, which is available at Barnes & Noble.
In that publication, there are many ads from companies that make parts and conversion kits for older cars.