1974 Duster Idler arm question,

This is a rare occasion where I have to disagree with Del.
There will be no issues putting the washers in to take out the slop and long as the washers go around the inner tube inside the arm, and are wide enough to support the shoulder of the arm pivot.
(This is how they did it brand new out of the box) and someone just failed to put them in.
The foam rings are just simple dust covers, and you can make your own if it comes down to that.

You can see by this picture that there is supposed to be a washer on each end, and it looks like the bracket in your picture has been squeezed closed a little from them not being in there.
I have fixed a crapload of these things with your exact problem.

This picture should give you a better idea of what is missing.

I should also add that you don't want the washers to pinch the arm, but just to take the extra play out of it with the retaining bolt and nut good and tight.
The bracket should pinch the inner metal tube, and not the washers or arm pivot.