The shouldered Allen bolts I mentioned are available on Ebay in a bewildering assortment of diameters and shoulder lengths, so you shouldn't have much difficulty finding something that will be a good fit. I'd also consider using a flanged nut on the thread side of the shoulder bolt for extra holding capacity. Victor has chucking reamers in .001" graduations below about .500" or so, which should make for an almost rivet-snug fit with a little tinkering to match up shoulder diameter and reamer size.
Jerry

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