Why is the steering wheel off center?

I just replaced my entire front brake setup (from 9" drum to K-H discs), including the lower ball joints, and now my steering wheel is cocked about 10 degrees to the left. The car still tracks straight, the wheel is just off center. I did not touch the tie rod adjustment at all -- I just popped the ends and bolted them back up to the new ball joint arms.

I don't think anything I did should have changed the alignment, so I can't figure out what would cause this. Unless maybe some component that I replaced was damaged, and the alignment had been set up to compensate for it.

Any ideas?