Classic/Antique Car Repair: 63 Chevy Impala, power steering problems, front end alignment

Question
I have restored a 63 Chevy Impala, 283 motor, automatic, no a/c.  New front end suspension installed, and front end alignment was done recently. Now, when I drive the car and make a right or left turn, my steering wheel does not come back, you have to manually, after the turn, turn the steering back to center. I replaced the whole saginaw power steering system. No leaks. Wheel turns easily, except after a right or left turn.

Answer
If the problem is only when the car is moving I would lean more to the caster and toe in settings than to the power steering problems. I would want to see the caster settings as close to 1 degree + as I could get them as it is caster that creates the self center action of the steering. The newer cars run upwards of +5 degrees of caster. If the toe in is set a little too much outside of specifications it too can cause the steering wanting to stay off center. Also radial tires which were not standard on this car require a bit more caster to get the self centering steering working. Radials tend to want to stay in the direction that they are pointed in.
Brad