Mike, a .003 feeler gauge passes fully through the gap, but the gap is not parallel. It tapers, so I don't have quite enough arbor length/ hole fill. I suppose I could take off a little material from the barrel in the area of the locator pin seats.
I've done several Pettifogger Dillon button arbor mods lately with decent results. A #2 Dillon button just starts in 1849 arbor hole, but the pin diameter is actually larger than the wedge slot in the arbor; both parts would need turned down. I didn't feel like that much effort and cast about my workbench area for something that might work. The washer keeps it from binding and didn't require any drilling, tapping, turning, swearing, or sanding. The JB Weld is to keep from losing the washer since I don't plan to load a Wells Fargo on gun. I put it on arbor instead of in hole so it'd be easier to remove if I decide on something else later.