68 power steering conversion,adjustments

I have restored my 68 and the lattest addition has been to change out the manual steering to the original power assist. I bought centre link, box, cylinder, pump, etc off ebay at about $160 cnd. All components are in good shape - box was stripped and relubbed, control valve kit installed.

At same time I have completely replaced the LHS frame rail from torque box forward. This gave me problems in obtaining services of a first rate alignment guy as most here will not touch anything where the frame has not been done by a frame specialist. The upper arm was removed and had to be shimmed out to get the camber right - cause is unknown but obviously something slipped or distorted. Shims are about 1/4" and basically car steers OK and straight. Control valve had substantial corrosion but cleaned up OK with fine emery paper. There may be some pitting at edge of one port that could be causing leakage. I have backed off the top adjustment on the box to see if the "sweet spot" was set too stiff - 1/8 turn did little. There is not much slop in the wheel and the linkage is tight throughout.

My problem is that the "feel" is not quite right and the car tends to wander. You have to pay constant attention to steering.

What should I try adjusting to correct this problem?

68 PS conversion

Thanks Dave:
The total system from box thro to tie rods came off a 68 and all appears to be tight.Ball joints OK etc etc. Only parts that is different is indeed the idle arm. The idler on the PS setup was seized on one rubber bushing and while I returned home to pickup the original manual linkage to swap out the idler, the guy (jackass) doing the alingment, burned off the PS idler rubber and removed the idler arm. We then discovered that indeed the PS bushing sizes are different to the original manual. The centre to centre appeared to be the same, so the fix was to ream out the bushing insert on the manual arm. This is now free to swivel on both bushings and "reasonably" tight on the 2 bolts/shafts . The odd thing about the idler is that there are "teeth" on one bushing inside tube - like its meant to not turn, but rather to grip the centre (drag) link. I defeated the teeth/grip by inserting a washer.

My assumption is that the idler simply holds the linkage assembly up and does not really take an active part in transmitting the forces from box/cylinder thro to wheels.

I have played with backing off the top screw (sweet spot adjustment) on the box and tightening the adj nut on the control valve and there is some improvement but it is still not right.