I wouldn't even look at the brake lines. I would replace all hard lines, soft lines, wheel cylinders, and master cylinder (if there is significant fluid showing under the rubber boot). These trucks don't stop real well when everything is perfect and new, let alone when something isn't right. But then I'm getting less daring than I used to be.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission