Sorry to ask the obvious, but you have tapped the quill bolt firmly with a rubber mallet until it drops back into the recess? The "shim" could be just the edge of the stem surrounding the expander wedge.
I don't think it would have a shim in it, unless for some reason they used an old Schwinn stem? They were small enough to put in a thin shim on a 22.2 steerer, but not likely.,,,,BD
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