Steering/Wandering while driving

I was with a friend of mine who have a 1971 with PS and PB. When we went for a drive the car seems to wander on the freeway. He's has had the front end rebuilt with all new ball joints , tie rod ends, HD pitman arm. along with new a arm bushings. Then he just had installed a new steering Box along with a new steering control valve and slave piston. Took it to the alignment shop, along with the balance of all 4 wheels and tires.
When he is driving on the freeway the steering wheel needs to be corrected by turning back and forth about 1-2 inches - back and forth.
So any Ideas as to why it still wanders?

Did he replace the steering shaft coupler? Often referred to as a "rag" joint.

Yes that was replaced when the steering box was replaced.

Maybe he got a badly rebuilt steering box.

This was all done on my 68 back in the 90's but I didn't replace the steering box. 

He doesn't just rebuild them, he blueprints them.  Better than new.

Has he had anything done on the rear of the car? Toe, and camber settings on the rear must also be done to keep the car tracking properly. I've spoken with a few Corvette techs that absolutely HATE doing rear alignments on these cars. Even at the dealer, they don't spend much time making sure it's right..."close enough" is close enough for some of them.

 I did my front-end, and only after doing the back did it behave correctly on the road.

|UPDATED|2/10/2015 6:06:35 AM (AZT)|/UPDATED|

Yes, it was a 4 wheel alignment. The Steering box was a Redhead from WA State.

|UPDATED|2/10/2015 10:05:58 AM (AZT)|/UPDATED|