Just picked this ole gal up the other day. She is very rough around the edges with 220,000 miles of Idaho farm life, but the thing is virtually rust free.
She needs just about everything looked at, but still manged to run and sort of drive so I have a good start.
The cable on the brake valve is the "hill holder". When the clutch is depressed it prevents the truck from rolling backwards while starting on a hill when you remove your foot from the brake pedal. IIRC it also connects to the clutch pedal.
Nice Brat BTW, cant wait to see what you do with it.