My '41 GMC used to have the same problem. The fix cost me nothing but time. I suspect a lot of folks spend a lot of money changing a whole lot of things that aren't really necessary. Sometimes, we get caught in the way of thinking that old technology isn't as good as new, and that may be true on a few things but not as many as one might think.
Bump steer, wandering, or darting front ends were a bad thing in the 30's, 40's, and 50's and the design of the front ends is good enough not to do that IF it is lubricated properly.
I spent several days cleaning the old, hard, dried grease from my king pins, tie rods and spring eyes. This not only made it look better, but it made an escapement for the grease to flow all the way around the joints. If the the grease can't get out, it can't get in either. I had to remove the fittings and in some cases, I took a paper clip and dragged out as much old grease from the fitting's hole as possible. I made sure the little spring plungers worked on the tips of the fittings themselves, and I unloaded the joints by jacking the front end up with the jackstands on the frame...NOT... the axle. This allowed me to grease the truck properly for the first time in 50 years! When I pumped grease into the king pins, I heard a thunk...that was the grease filling the dried gap between the kingpin and its bore (yes, there must be a gap or in won't work). The same held true for the tie rods and the spring eyes. When I saw the same color grease exuding from ALL the way around the joints as was in my grease gun, I stopped and wiped the excess off. Sometimes, I had to wiggle the axle, tie rods, and springs to get the grease in and ALL the way around the joints.
When I drove the truck after doing this, I couldn't believe what I was feeling. The truck did not dart around when I would move to the shoulder of the pavement during a turn. It no longer wandered. It held straight down the middle and no longer had my nerves on end. It felt safe, solid and dependable again.
My theory is that with dry joints...kingpins, tie rods, and spring eyes...any jolt tends to make the joints stick into whatever position they are bumped into...in other words they can't tolerate a momentary jolt in a crazy direction and imediately return home. Proper greasing allows all the steering geometry to work like it was designed to work. Safe handling is not something that is new in this day and time. It was important in the 30's 40', and 50's too.
The evolution of the ball joint and better rubber seals made the old kingpin technology seem obsolete because the seal in the ball joint pretty much never allows the joints to go dry...and coil springs don't need lubrication...so it makes old technology look bad and obsolete.
