I've been through a lot of Idler arms in the last 17 years.
I have run into the same issue with washers being apparently too thick, ,and if one leaves out one washer then the idler can move up and down in the fram receptacle and if one just clamps the recptacle with the bolt then there is metal on metal with very little load spreading support. The Washers have to be in the inside, on such designs
I do not remember if it was on my most recent set of Idlers, or my previous set, but I had to open up the frame receptacle to get washers top and bottom. I used a grade 8 bolt and a few bits and peices to stick inside the receptacle, then unthread the Nut effectively stretching the receptacle box to accommodate the two washers.
My latest Idler arms are theh Moog Problem solvers, and I lucked out with the old made in the USA stock. They have the Grease zerks on each pivot point, as opposed to only on the part which fits into the center link.
These Moogs have been in there since 2011 and I can detect no slop, just greased them last week or so.https://www.rockauto.com/en/moreinfo.php?pk=203133&cc=1073506&jsn=449
In the picture above, the three thicker 'washers' are foam rubber grease retainers.
I did prep and paint then with appliance epoxy before installing.
Anyway its is not hard to make ones own spreader with a bolt some washers and a nut, and open up the receptacle just enough to fit washers top and bottom.
If there is no grease zerk on this pivot point, make sure to grease both sides of the washer, and the interior where the large bolt resides and the bolt itself.
If installed dry they will get sloppy pretty quickly and no doubt contributed to the very poor life I was getting from local auto parts stores parts.
The AC delco design seems like a cross between the washers required and no washers required designs.
I've used both, the Moogs have given me the best lifespan so far, but it might be because i got the older made in USA stock.