I see. It won't hurt anything to shift it manually, but you may try seeing it does still shift automatically. Put in "3" and see if it will shift through the gears normally.
However, before you take it out on the highway again, you might look into the steering and brakes, see what's going on there. The steering could simply be an adjustment issue, just based on the description. I don't know if you've ever adjusted a Saginaw type steering box before (I'm assuming it still has the manual steering box), but here's a quick rundown of how to do it. On the side of the box, opposite of the pitman arm, you'll see a slotted screw with a jam nut. Take the nut loose, then turn the screw in until the play is almost completely gone. You don't want to go too tight, there should be a very slight amount of play. Hold the screw and tighten the nut. The wheels should be pointed straight ahead when you do this. If there isn't any play in the box, then you'll need to check for worn steering parts, the pitman arm and idler arm are the two main culprits for what you're feeling.
Same deal with the brakes, check for worn linings, leaking cylinders, proper adjustment.
Got to make 'em stop and steer before you make 'em go fast!
