Classic/Antique Car Repair: 1972 Datsun 510, front wheel alignment, datsun 510

Question
Hi there, my car has a steering problem...I went to get an alignment done on my car(twice) and I do NOT like how the car steers...My problem that I'm having is that after left hand turns my steering does not "self correct"...my steering does not come back over after left hand turns and then it drives "piggen toed" untill I take a right turn and then the steering gets fixed...now I have done alot of modifications to my suspension...BUT all my modification were done properly...I have changed to Willwood disc brakes all around, and I have change the whole suspension to a 2012 coil over all around...now I wanted you to know that when I lowered my car I had to put some new stuff in aswell...under the car near control arm and had to get "bump steer spacers" to fix the geomentry of the control arm...also I had the newest 2012 camber plates installed at the top at the strut tower...After I got the first wheel alignment done it was really shitty! I went back to them and told them...my steering wasn't self correcting after "left hand turns"...SO the mechanic said to me" Sunny we can only do a front wheel alignment on this car(not 4 wheel)" and then he said "your Datsun 510 does not have a way to do adjustments"...I pointed out my new camber plates and the bump steer spacers...he then said "Sunny all that stuff is good, and it helps alot, and it works, BUT this car does not have CASTER ADJUSTMENT"...he told me to buy somme adjustable tension rods if possible...so my car is 40 years old and I got a machinist to fabricate some custom Adjustable tension rods(decent job)....I went to the Alignment shop and he said "ok, I will install these and set it up"... but even after the adjustable tension rods are in, I still have that same problem..its BETTER with adjustable tension rods, BUT the steering is not self correcting after left hand turns. Do you have a suggestion for me. Thank You  Sunny

Answer
If this is power steering it sounds like the steering gear (or rack and pinion) is worn out internally. My guess it that the torsion bar in the input shaft is bad and is not returning the valve to it's center position. A good quality rebuild should take care of that.