Steering boxes

[Fast68Chevy]

P/S gear box is trash on the 81 C-20.
Pitman arm is worn a little...
Can this cause the front end to shake/shimmy badly when the brakes are applied ???

Are steering boxes on the 78 C-10 same as on the 81 C-20??
Part numbers in catalogs say no, but whats the difference ??
And how do I know when the pit arm is, correctly, on the output shaft of the box
when replacing the arm ??
I replaced the 78's arm, and ever since then, the truck turns farther to the left, than to the right.
The steering wheel was crooked (not centered) since before I got the truck, but didint have this problem, then... Otherwise the truck drove straight as an arrow, no sloppiness whatso-ever...
I tried taking the arm off and centering the wheels and the steering box, then reinstalling the arm, but it wont fix it...
Are the 78's and the 81's arms and boxes the same ???
I apreciate any help on this.... Got to fix this soon, or a blue 81 C-20 is gonna end up in a ditch, somewhere, in a bad way...