Did you remove the steering wheel, and was it straight before?
If you didn't take the wheel off, then I would leave it alone...that ain't the problem.
Most steering boxes have a "flat" on the shaft that the rag-joint/column attaches to. There is a corresponding "flat" on the rag-joint. That should make it self explanatory...just line the flats up.
However...if your rag-joint doesn't have a flat, then we gotta just line it up best we can without it.
Make sure the front wheels are dead-straight ahead. Then, disconnect the rag-joint, and turn the steering wheel straight up, and re-assemble. That should get it straight. If it is off just a little, then you may need to have the front toe set at an alignment.

If you took the steering wheel off, or even if you didn't(someone else may have in the past), all you have to do to check it is pull the horn cap off, and look. There is a stamped "line" on the wheel, AND the steering shaft, where the nut goes on. If ithe two lines are not lined up, you'll need to remove the steering wheel, and turn it to line the marks up.

The '63 to '68 boxes did not have the flat that Joel describes.  To be correct, your box should have that flat, but if you have an earlier version, align it like Joel described.  But just to be sure, I would first count the turns lock to lock, then go half that number back to make sure the gear box is centered.  Then see if the wheels are straight.  If not, you should be able to adjust toe-in to re-center things.

Larry

[QUOTE=VetteSpecialties]The '63 to '68 boxes did not have the flat that Joel describes.  To be correct, your box should have that flat, but if you have an earlier version, align it like Joel described.  But just to be sure, I would first count the turns lock to lock, then go half that number back to make sure the gear box is centered.  Then see if the wheels are straight.  If not, you should be able to adjust toe-in to re-center things.

Larry
[/QUOTE]

I would first center the gear box by counting turns and splitting the difference.  Then see if the wheels are straight.  The Pitman arm can only go on one way, so if the wheels are not straight, you need to adjust the tie rods to center the wheels.  Now you can worry about centering the steering wheel.  Maybe any or all of those parts have been apart in the past, so the problem could be anywhere.  Besides the splines on the rag joint, which you say have the flats that should make them go on correctly, there are splines on the top of the steering column where the steering wheel goes, and the steering wheel has all those screws around the edge of the hub where it could have been moved.

I went through all that when I removed aftermarket Rack & Pinion from my '71.  The important thing is to start with the steering box centered, then match everything else to it.

Good luck
Larry