Anything you'd like. You can try to figure out the stock setup, but unless you're trying to restore to original condition for nostalgia or sentimental reasons, you can go with whatever works/is easiest for you.
A solid metal rod with drilled holes at the end would keep the brakes stiff.
A steel cable would do the trick also.
Just make sure whatever you use is hooked up solidly.
The only other thing I can think of is the brake pedal returning after you let off the brake. Does the pedal have a return spring? Or is there some type of spring helping pull the brake rod back after it's pushed?