If the play was just in the steering box the car shouldn't be a problem to keep straight in a lane, it should go straight all by itself. More than likely you have a combination of worn out steering parts, a not so great alignment, and some extra play in the box.
If you have a manual box, which is sounds like you do if you're considering a 24:1 or 16:1 replacement, then there's a screw on top of the box with a lock nut. If you loosen the lock nut and tighten that screw it will adjust some of the slack out of the box. But if you over adjust it you can also make the steering gear resistance overly tight.
The ratio does determine how many turns the steering has lock to lock, it also determines the amount of force you need to turn the wheel. A 24:1 steering box is roughly 5 1/2 turns lock to lock, a 16:1 box is ~3 1/2 turns lock to lock, with that much less mechanical advantage. Both were available from the factory, the 16:1 boxes were only offered for a year or two if I remember right, the 24:1 box was standard. You can replace a 24:1 with a 16:1 without changing any other parts, but from the sound of it you should be considering replacing the pitman, idler, and tie rod ends anyway.
