These cars used DOT3 brake fluid. It attracts water. The brake cylinders and pistons are bare steel. Picture water sitting against bare steel for all those years. The pistons inside the cylinders could (likely but not guaranteed) be rusted in place. If they're in the brakes released position and rusted in place you'll have no brakes when you step on the pedal. If they're in the brakes applied position the wheels will be locked. If, by chance, they're not rusted in place, the cylinder wall will likely be pitted and when you press the brake pedal fluid will leak past the seal and you'll lose all the fluid. Plan on doing a full brake job before getting the car on the road.
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