An improperly aligned car can result in many undesirable driving and handling characteristics. Poor on center feel can be caused by toe-out or unbalanced caster. Improper alignment can also sharply reduce tire life and cause improper wear patterns.
The SHO should be aligned with neutral toe (zero total toe) and as much caster (about +4 degrees is available) as possible. This may mean freeing the spot-welded camber plates and moving them to their most rearward position(s). Ideally, caster should be balanced side-to-side. Camber should be -0.5 to -1.0 degrees per side, also balanced side-to-side. Camber more than -1.0 degrees, will accelerate inside edge tread wear. You may find it difficult to get a shop to align to these specs, most won't change anything if it measures somewhere within the tolerance windows. A $20 'tip' to the alignment tech sometimes helps.
The Ford recommended way to free the camber plates is to drill out the spot welds with a special cutting tool that can be obtained from Speciality Products of Longmont, Colorado. Speciality Products is a major supplier of alignment kits and tools to the automotive alignment business. The spot weld drill is called the Taurus/Sable Rotor-bor, part # 85790. It is designed to drill out around the spot weld on the plate and leave the strut tower sheet metal untouched, which is important to maintaining the strength of the strut tower. It costs about $10. Speciality Products can be reached at 800-525-6505.
Rear alignment for the street and for even tire wear: Camber, 0 to -0.25 degrees per side; even -0.5 degress will give some inside edge tire wear, especially on soft-compound performance tires. Toe, neutral to slightly toed-in, 1/32 per side is good. The soft bushings in the rear tension struts tend to let the rear toe out when moving forward and during cornering, so some static rear toe-in gets you to neutral on the road. Make sure that the lock washers are installed in the bushings and the lock screws are installed after the alignment is complete, and that the bushing bolts are hand torqued to the spec supplied by Specialty Products. Otherwise, the bushings may slip out of position.
In '89-'92, the Taurus had only toe adjustment on the rear. This was accomplished by an eccentric on the rear control arm. Camber adjustment was added by TSB 93-1-2, which released a camber kit for the rear suspension. This kit uses some hard PVC eccentrics that replace the inner bushings on all 4 rear control arms. These allow up to a 2 degree camber change and a 1 toe change per wheel.
The Ford part number is E7DZ-5K751-B. Specialty Products also makes the Taurus/Sable rear camber/toe eccentric kit, part # 87300. Cost is about $45. Sedans built after '92 already have this kit installed.
If the tech can't adjust camber and toe with the TRW pieces, then the original toe eccentric may be frozen from rust, in which case it will need to be replaced.