The alignment is set by the upper suspension arms sliding in slots to adjust the angle of the front wheels, then the arms are tightened into position to stay... theoretically.

The one on the left front continues to slide around even after it is tightened down.
I'm not sure what to do about it yet. He tried some spiked lock washers, and a couple other tricks that didn't pan out, so i took both arms off to look and compare.
They dont look that different. There was a little more dirt packed in on the left side where the arm bolts to the frame. That might have been the initial cause, or it wasn't tightened down enough one time, and the more it slid, the more it wore down the ridges which hold it, making it worse.
It may also have thinned the frame a few thousandths of an inch there too. I know that doesn't sound like much, but it could be enough to matter.
I have a couple things in mind, but i want the input from the owner, Jason, and from my brother, both of whom are very smart.

Being a mechanic by trade doesn't always mean i know the best thing to do on someone else's 38 year old car, esp. when no one else seems to have run into this problem before. I think between the three of us, we ought to be able to decide on the best course of action.

Here's some pics of the left front arm and frame where the bolts go through. The right front looks about the same, except not quite as shiny on the frame.