I subscribed to the other thread you started because I have the same issue.
For what its worth...I swapped out my steering box for the factory 1972 box. My issue was slightly different, I would turn the steering wheel left and it had a lot of play. Then all of the sudden, wham, it would dart across the street. The new box fixed that issue.
The other items: Bumpsteer and wondering. (I have the same issues) My guess is its the way the truck was lowered. Your front spring is maxed out because that's how the PO dropped the truck to get it lower. I think that is causing the bumpsteer problems.
For my truck, I'm going to swap over to a drop spring and see if I can get the angles of the suspension to work better.
Here are some pics that helped me. My guess is that your truck (and my truck) have angles that look like the bad sides of an isosceles trapezoid
http://67-72chevytrucks.com/vboard/s...ight=bumpsteer