Having been on an idler arm odyssey myself with my vans over the years, I can empathize with your plight. On my vans, for example (all of them....3 from the 80's, one from the 90's, and two from the last generation), all of them had washers situated inside the frame bracket, on the top and bottom of the idler arm shaft. Occasionally, the washers did not fit this way with a new arm, so I would substitute one that was just a hair thinner. Ideally, they will have to be tapped in place very lightly with a hammer, and lined up as best you can as the "idler arm sandwich" is coaxed into the bracket. I assure you without any doubt that there is no harm in substituting a slightly thinner washer, so long as the fit is snug. I have done so many of these on so many Mopars, I can hardly recount them all. It's become so ridiculous, I have a small stash of washers just for idler arms kept separate from other hardware. There are a couple of other ways to do this, I guess, but the idea of spreading apart the bracket always kind of made me apprehensive.