The lower control arm bushings could be worn badly and you would have a hard time noticing with the spring tension. If they are worn, every time you hit a high or low spot in the road the arm shifts and changes the geometery of the front end. This will change the alignment and make the car wonder. I believe this is one of the most common problems with a loose front end in a first gen Bird. I have found it on show cars that you would think had perfect bushings but just have never had them changed.
Jim