Master Cylinder Autopsy

Not sure how original you want the car to be but that looks like a single piston master. For safety sake, I think I would replace it with a dual piston and run new brake lines as needed.

If you do decide to do that, I would really recommend using DOT approved copper/nickle alloy brake lines that are available and the reason is because they are extremely easy to bend, double- flare and believe it or not, they don't work harden so if you make a mistake you can re-bend.