This is the process I used for my K25.
- verify the center point of the steering box by counting the turns full left and right, and then back to center.
- check the position of the steering shaft and rag joint. On my '75 the steering shaft has a flat section, and it points straight up at the center point. I'm not sure newer trucks have the same orientation.
- with the box and shaft centered, the wheel should line up close to center unless you got it installed off to one side. I punched a divot in the wheel and center shaft to mark the alignment before pulling it apart, but its probably too late to do that now.
- use the drag link adjustment to put the wheel at exact center.
If you then drive the truck slowly forward in a straight line on a smooth concrete surface, the wheels should self-center. Then recheck to see if you also got the steering wheel centered.
Bruce