Early twin I-beam axles were notorious for wander/wobble. You hit on a couple of things already that can cause that problem, the sloppy steering box(biggest offender) and ancient (and probably useless) shocks. Also, another area is the 'rubber' pad/bushing where the two struts meet up at the frame. Occasionally the bolting or rivets that hold the bracket to the frame are worn as well. Also, this was a high rust area. Water and crud were trapped there. The bushings on the axle frame ends themselves could be shot. Then, of course, the king pins. Unfortunately the guy at the alignment shop, unless he is a REAL old timer, most likely doesn't have the experience to deal with the old Fords. Unless these shops have specialized equipment, all they can do is set the toe. Caster and camber require hydraulic axle bending tools to adjust - and very few shops ever had those tools nor the skills to bend the axle right.